I am caring for an elderly man who can't talk to me but tries and gets frustrated. Do I try to figure out what he is trying to say?

This is so incredibly sad - and common. First, imagine yourself in his situation and how hard it is for him. That will help keep you calm.
Secondly, there is no way you can fix this, so don't feel guilty.
Comforting by holding his hand and looking into his eyes to show you are tyring to understand will help sooth him some. You may want to read this article: How to Communicate When Your Elderly Parent Can No Longer Speak at https://www.agingcare.com/134129
You have a caring heart - that I can see.
Carol