You mean enter the contest? Or to join the game?

You can join the game here -> https://www.risingstargame.com?referrer=freedomprepper

Easiest thing to do is just register and start the first mission.
Read the FAQ section first.
When you have a functioning Rising Star Account, your are already in the contest, as you have commented on the Giveaway.
This was your entry.
It is stated in the rules of this post.