Deepweb

I keep reading up on things about this "hidden web" hidden wiki, darknet, deepweb and .onion. is incredibly confusing and i know the basis, something under what is readily searchable or hidden. alot of sites point to this as being illegal or filled mainly with illegal things, CP, assasins ect. anyone have experience? is the deepweb inherently illegal? is there a way to access this if it isnt? how does one exactly using TOR access .onion sites?