You contribute with Tron ( TRX) or with seed ( a token on the tron blockchain)
What you get can be found in this post: https://steemit.com/sesameseed/@sesameseedorg/seedgerminator-update-to-splinterlands-listing-contributions-and-incentives
You do not get anything now, I think it`s about 2 months out. 4 new promo cards will be released