How do o I obtain get a credit card under new law? Under 21?

Im 18 and don't plan on getting a credit card until im 19 or 20. This new law seems to make it harder for teenagers to get credit cards. Its good is some cases. But I will need to build credit by 20 and I was wondering how do i obtain a credit card. i know you may need a co signer. But i know if you have sufficient income you can get one. But my problem is what do they me my sufficient. I know it means I will need to prove thai I will be able to pay the bill on time. But my problem is what do they mean. I am starting a job at a grocery store for like 7.50 and hour. But is that sufficient enough and how will i be able to prove that when I apply for a card online or at a bank.And please don't say not going to happen and the law states so because i read what it says it just said i cant get one if i don't have proof of income or co signer. My problem is what is that proff of income and what i stated above good enough to start building credit and get a card. Thanks