RC stands for research chemical, as you probably know. Its tons of different substances each with different effects. The most popular are psychedelics, stims, opioids, benzos, dissos, empathogens, etc. Pretty broad term really, so a pretty broad question. Most are intended to be mimics of classic drugs but some also have entirely unique effects (some of which are not desirable). If you narrow down what you are interested in specifically, more people will be able to answer your question a bit more thoroughly. RCs are mostly about legal work-arounds but there are some novel compounds that some enjoy as much as the classics. If you browse around the different forums you should be able to get a feel for what they do.
Cheers mate.