I am new at this field, what if all biitcoins were already out, 21 million of them?

All BTC are not out.
There is an emission curve that allow xx BTC to be created every block so there is a limited & predictable quantity of BTC created every day/month/year.
There will never be 21 millions BTC in circulation because many of them are already lost. Any BTC lost cannot be recovered.

Have a look at some videos if you are new :
https://www.youtube.com/watch?v=Um63OQz3bjo
https://www.youtube.com/watch?v=Gc2en3nHxA4
https://www.youtube.com/watch?v=GmOzih6I1zs
https://www.youtube.com/watch?v=ZT26y_l-jtI

Thanks for this info @superresistant, I thought that all of them can get out and will crash the value or something, so some of them get lost too?wow.