I got approved for a credit card and now another credit card company sent me an pre-approved application...?

No, you didn't get a pre-approved application. You got a pre-selected application. You fit the general criteria for the mailing list. It is very possible that you will not qualify for the card in that offer

If you have just gotten the first credit card, wait at least 6 months before you apply for another. You don't need to apply for every credit card that comes along. Read all the terms carefully. Not all card offers are alike.

Best way to build your credit is to use that new card for regular purchases, wait for the statement, and pay the balance in full. That will build your credit and avoid interest. In about a year you should have enough credit history to qualify for a better card.

Another thing to keep in mind. Just because someone sends you a "pre approval" does not mean you are approved. It also doesn't mean that this is necessarily the best card for you.

Whenever you get those in the mail, shred them, don't just toss them in the trash. I went to the 3 credit bureaus & opted out of any new offers to be sent to my home. I apply only when I want to & with the card I have chosen after much investigation.

All you need is one card.

Careful with opening more than one card every 6 months.

"New credit" reduces scores for the first 6 months.

Use this card wisely.

Charge small things like food or gas and pay in full each month.

Remember: It is 100% myth that carrying balances is good for credit - nothing could be further from the truth

One Credit Card is fine, just make the entire payment on time every month.