What are the best yoga poses for a beginner to try and learn how to do?

Here are some. Illustrations appear after the text.

Start very slowly and stretch with the breath. Try a few and see how they feel. Listen to your body. If it says, “Don’t,” then don’t. Don’t be heroic either.

There are yoga classes on YouTube you can try.
Tadassana is a basic standing pose. Downward facing dog is done at every class I’ve ever been too.
You might also want to YouTube the hip sequence and the morning sequence.
I like iyengar yoga because it is really safety focused and uses props so you can do the poses correctly even if modified.

Child pose. It’s a great pose for a beginner to return to when the going gets too tough.

A beginning yoga class is probably your best bet. That said, I think sun salutations incorporate a lot of important yoga elements, including attention to breath, and they can be modified for any level of difficulty.

I agree with @sarahsugs re: sun salutations. They give you some variety and I personally always feel incredibly peaceful after completing a few. If you can do your yoga class outside, I also recommend that.
Some fairly simple poses you should be able to do without much experience: downward dog, child, cat/cow, warrior, cobra (gently. keep your stomach on the ground.)

It took me six months to get comfortable with sun salutations!

Look up the “Five Tibetan Rites” on Youtube. They’re very simple and calming.