How to start with leg stuff

Hi, I'm interested in broadening my horizons in terms of leg positions/ entanglements/ configurations.

I am not sure what to look for though. When I go to YouTube I mostly find attacks and how to finish submissions, but I have no clue how to even get there or what the position is called.

What are the main positions I should learn to attack/ escape from?
Thanks!

PS in case this makes a difference: I mostly like to play top positions (takedown, pass, top control)