I haven't received my 2nd or 3rd stimulus yet can you explain why?

The 3rd one is just coming out now.  Keep waiting.   You can check it here,
https://www.irs.gov/coronavirus/get-my-payment

If you didn't get the 2nd one you claim it on your 2020 tax return unless your 2020 income is too high and you don't qualify for any more.  When you go through the federal review tab it will ask how much you got if any. Or to enter your stimulus payment in TurboTax, type "stimulus" (without the quotes) in the Search box, then click the link that says "Jump to stimulus." Say no to the amounts it shows you. Then 2 boxes will open up for each round. If you didn't get one enter a 0 in the box.

After you have entered your tax information and are ready for the Federal Review, it will be the first question.

If you are trying to trigger it, you can go to Other Situations, answer any questions and click Done. The next automatic selection is Federal Review and it will ask about payments received.

The Recovery rebate credit is on 1040 line 30. It either adds to your refund or reduces a tax due.