[@Shovel]
I would say quite a bit, as we're taking from different universes it is highly recommended to have some knowledge about it. My best recommendation for learning about it is just browsing the Gundam Wiki and reading up on the tv series (Mobile Suit Gundam, Gundam 00, Gundam SEED/Destiny, and Gundam Iron Blooded Orphans are the most popular series with differing universe situations.) The basis of what to know is the series revolves around young adults (usually preteens) getting involved in a space war with giant robots (roughly 18 meters average). There are beam/laser weapons and telepathy like abilities as usual staples of the series along with anything called a Gundam being an prototype/advanced machine.

If you pm me I can explain more in depth if you are interested but if it's too overwhelming to learn and join, I understand and I don't want you to waste time learning about something you're unsure of.

Edot: I should clarify as this rp will be taking place after everything; events, people and places from the series aren't necessary to know for participation. Only things such as beams, generators and mobile suit types are a good start. Things can be explained in character if you wish to join and not be overloaded.