If I'm trying to describe a situation in the past in which I wasn't able to find a specific pair of shoes, should I say:
- I couldn't find those ones.
- I wasn't able to find those ones.
In this specific case, "can" and "be able to" are interchangeable. But be careful, because there are subtle differences.
For example, your question start with "Can I use..." - this is an example of using "can" with the meaning "is allowed to". Consequently, "can you do it?" may have a very different meaning from "are you able to do it?", and sometimes you should choose your words carefully.
You can use either.
I could not find something.
I was not able to find something.
"Can" means ability.