Manipulation
The base foundation for all jujutsu is a jujutsu user's ability to control their cursed energy and use it to carry out certain functions, such that there is a massive difference between just being able to sense jujutsu and actually being able to use it within the world of Jujutsu Kaisen. For example, some people are able to sense the "pressure" of cursed energy in their environment, but don't really know, recognize, or understand it, so they are not able to utilize it. Sometimes, during life and death situations or when an individual is filled with strong emotions, they may be able to sense this pressure more easily and maybe even utilize cursed energy in combat while in this overwhelmed state, but likely would not be able to repeat it again in a calmer situation a few days afterward.
Generally, control over cursed energy requires innate skill and vigorous training - it even requires practice to control one's emotions while simultaneously controlling cursed energy. In some instances, sorcerers may train by constantly imbuing cursed energy into an object in order to learn how to manipulate their cursed energy with control.
In Jujutsu Kaisen, some have compared cursed energy to electricity: it's volatile in nature and difficult to use in its rawest form. For example, while raw cursed energy can be used for its blunt force, it's best used by sorcerers to power their techniques in the same way electricity is best used to fuel electronics. In this sense, cursed energy is channeled into a technique to activate a sorcerer's unique abilities. However, cursed energy does not flow on its own and sorcerer's can experience difficulty moving cursed energy throughout their body, especially when inexperienced.
Most importantly, proper control over one's emotions is key to channeling cursed energy and every jujutsu sorcerer is trained to do this so they don't waste their power supply even while they're overcome with emotion in the heat of battle or otherwise. As a result, it's been noted that sorcerers leak so much less cursed energy than the average human, that if every human were a sorcerer, curses would cease to spawn. Due to profession, personality, and other characteristics, there are differences in how various sorcerers, and even non-sorcerers, use cursed energy. While cursed energy leaks outward from non-sorcerers, it flows heavily within sorcerers which keeps it contained.
Most sorcerers instinctively believe the origin of cursed energy flow starts from the negative feelings in their stomach and flows through the rest of the body, but this model imagining one's body as different sections delays the flow of energy. In order to understand this cycle, one must realize that they exist in the world with their entire mind, body, and soul as one. For instance, an elite sorcerer has greater accuracy in controlling cursed energy so they evenly distribute their flow across their body, making their attacks hard to predict until the very moment it's executed.
Application
Offensively, applying cursed energy to physical attacks can be as effective as a cursed technique when it comes to gifted close quarter combatants. For instance, there are some sorcerers without a technique that use a union of cursed manipulation and physical prowess in order to compete with stronger foes. Meanwhile, powerful cursed spirits can utilize raw cursed energy as an explosive energy field to attack. For example, some can launch their energy as a projectile or even erect cursed energy barriers.
Defensively, users can coat their skin in cursed energy to protect and harden their body, increasing their ability to block incoming curse-related attacks. Although slightly different, this application is similar to the offensive application outlined above where the user imbues physical attacks with cursed energy to increase their destructive power to superhuman levels.
Utilitywise, conventional weapons can also be infused with cursed energy to increase their strength, similar to the method of training mentioned previously. However, imbuing too much cursed energy at once can compromise the objectls integrity and destroy it, so one must be careful to only infuse small amounts of energy at a time. Using this method, imbuing moderate amounts of cursed energy over time can transform a normal weapon into a cursed tool.
Black Flash
Black Flash is a special phenomenon in jujutsu where the application of cursed energy within 0.000001 seconds of a physical hit which creates a spatial distortion that causes the (usually blue) cursed energy to flash black, in turn multiplying the destructive power to strength equivalent of a normal hit to the power of 2.5.
In order to unleash Black Flash, it requires such incredible concentration that there does not exist a jujutsu sorcerer capable of doing so at will. Despite what some may think, this does not occur randomly and requires immense skill and combat potential to pull off. It's commonly thought that those who are able to use the power of Black Flash more frequently are blessed by the sparks of black. Interestingly, since Black Flash is simply a special phenomenon of advanced cursed energy manipulation and application, protagonists, antagonists, and even cursed spirits are capable of performing the technique regardless of their alignment.
Furthermore, those who manage to unleash Black Flash immediately gain an advanced understanding of cursed
energy far beyond those who have not. Moreover, anyone who succeeds in landing Black Flash will temporarily
enter a state of increased cursed energy awareness, where the mental process of manipulating cursed energy
becomes as simple as breathing for them. Consequently, performance in combat is greatly increased, allowing
the user to operate at 120% of their maximum potential.
Reverse Cursed Techniques
As a bonus, here's a little extra about reverse cursed techniques. We already know that cursed energy is born from negativity, which means human flesh can't be regenerated from it even if it can be reinforced. However, by multiplying this negative energy together, positive reverse cursed energy can be created. Such a feat can only be accomplished using a reverse cursed technique, which is a special type of cursed technique that requires extremely complex and sophisticated cursed energy control. Essentially, this is a very complex technique that is mainly used to heal human bodies through precise manipulation and application of cursed energy.
As a result of taking two sources of cursed energy and multiplying them by one another, the "energy that destroys" becomes "energy that creates", and negative energy becomes positive. Despite sounding simple enough, producing reverse cursed energy is extremely complex and difficult to perform for most jujutsu users. Although reverse cursed energy can be used for various purposes, it is most commonly used by jujutsu sorcerers for generating new flesh to heal human bodies. While very few sorcerers can utilize a reverse cursed technique, there are even fewer that use it to heal people other than themselves.
Interestingly, since cursed energy comes from negative emotions it is unfit for healing living things; however, cursed spirits (which are made of cursed energy) don't require a reverse cursed technique in order to heal. As you'd expect, cursed spirits are vulnerable to reverse cursed energy as the positive energy can compromise the integrity of their negative cursed energy based bodies. Thus, when reverse cursed energy is blasted directly into a curse, it compromises the structure of their body and causes them to disintegrate.