Hey, I'm a newbie

Sup guys, I'm a newbie. I've not played DnD games for 13 years. What prerequisite stuff do I need to know before I start a game?

That depends entirely on the game system (if you're interested in playing D&D, which version?) and your GM. Knowing the rules is a good start even if you don't have a game lined up, but make sure to ask your GM what he or she expects of you before the game begins.

There are 100's of different brands/types of games around nowadays, even several versions of DnD. Do you know which edition you played 13 yrs ago, and if you wanted to play the same one (say maybe you remember it fondly, or you still have the books)? Or if you are up for learning other editions, both older and newer ones, you might want to spend a little time getting familiar with the range of different games & the range of different DnD editions, and decide what appeals to you. Then look on Roll20 for games of the flavor you want. Or another approach is look for games on Roll20 that are taking new players, and start learning whatever game system that game recommends, and ask the GM of it what you'd need.

13 yrs ago could have been 2e or older. There is a community that is specialized in the the older systems. I don't have the link handy, on a tablet, but it is called "Inn of the Welcoming Wench". Give a looking for group search (blue banner up above) a search for it. Ok made it home and here is the link : Inn of the Welcome Wench . It will take you to their listing page and just follow the instructions in the sticky thread to join. Good luck and have fun.