Using the Verb "to be"

The verb "to BE" (am, is), have the past forms (was + were)

But, the verb "to BE" is sometimes conjugated as been, being. Could you please explain this form? What form is it, and when is it used?

Situations like:
"Being a student can be stressful."
"He has been doing well in that class."

Another doubt I have is, when we use could, should with the verb "to BE". When we use "could" or "should", we shouldn't use the verb "to BE", correct?

Here is an example:,
"Actually, you could do very well."
"Actually, you could be do well."

Which is correct and are there any situations when I can use "BE" after "COULD"?

Everyone appreciates your kind help Ola and thank you so much.