You have to get at least Jr. Member of your bitcointalk account. Its a must to rank up your account because of most of the bounties required at least jr. member and up. Once you rank up, you have to look for bounty or signature campaign that suits your set of skills like translation, social media promotions and many more. You have to finish your task in order to get your rewards/tokens/coins and of course, you have to follow rules and mechanics of every bounty.