I have briefly introduced the different varieties and aspects of Nen in the novel, here is some more on the rest of it, it could be considered some spoilers, so you are hereby warned.
I will gradually update this if there are more about how Nen works, if you really want to figure out everything, just go to the site I got this from. Everything is written in much better detail there.
gotten from: Hunterpedia
Advanced Techniques of Nen:
Gyo (凝, Focus) is an advanced of Ren by which a Nen user concentrates a larger than normal of their aura into one specific body part. It increases the strength of that one body part, but leaves the rest of the body more vulnerable.
In (隱, Conceal) is an advanced form of Zetsu used to render one's aura imperceptible, effectively concealing it. Unlike Zetsu, however, In does not stop the user's aura flow; instead, it hides it, making it impossible to perceive with any of the five senses or extrasensorial
En (圓, Circle) is an advanced of Ten and Ren. In Ren, aura usually envelops only a small amount of space around the user's body. En is when one extends their Ren so that their aura extends further than normal, then uses Ten at the same time to contain and give shape to that aura, normally a sphere. The minimum requirement is to extend one's aura to a radius of more than 2 meters and hold it longer than 1 minute. Someone using En can feel the shape and movement of anything within the area covered by their aura, with the degree of awareness and finesse depending on their level of skill.
Shu (周, Enfold) is an advanced of Ten. Shu allows a user of Nen to enshroud an object with their aura, allowing them to use that object as an of their own body.
Ko (硬, Temper) is a of Ten, Zetsu, Hatsu, Ren, and Gyo in which all of the user's aura is concentrated into one body part. Gyo is utilized to focus aura on a part of the body, while Ten is used to prevent it from dispersing. Zetsu is used to completely stop the flow of Nen in all other parts of the body, increasing the output in the desired area. With Ren, the amount of aura is increased even further. This makes that one body part extremely powerful, but at the cost of leaving the rest of the user's body completely unprotected. Due to the risk it carries, Ko is regarded as a purely offensive technique.
Ken (堅, Fortify) is the advanced of the basic Ren and Ten techniques. It is a primarily defensive technique where a Nen user maintains a state of Ren for a prolonged amount of time. The amount of aura surrounding the user's body during Ken is about 10 times higher than during Ten. Ken allows a Nen user to guard against attacks from any , but the large amount of aura produced makes it tiring to maintain.
Ryu (流, Flow) is the term for use of Gyo from a state of Ken to perform real-time offensive and defensive value adjustments. If Ko devolves 100% of one's aura to offense or, much more rarely, to defense, and Ken splits it evenly between the two, Ryu is redistributing one's aura to any other percentage.