RUST Jackpot is a game in which players put their RUST skins into the pot to have a chance to win the whole pot. Users that deposit skins that are worth more will have a higher chance to win. Each pot is about 60 seconds (it depends on the site). In that time everybody can join the pot. After the time ends, the winner of the pot will be randomly selected. You will see a rolling animation that will indicate who won the pot.
Some RUST jackpots implemented backpacks, which you can deposit your skins into. Then you can directly bet your skins from the backpack instead of accepting steam trade offers every time you want to place a bet or you win.
Some RUST Jackpots are offering bonuses for new users, most commonly in the form of free coins. On most sites to get the bonus, you will have to log in and use a referral code.