Explain, Review, Refactor, Debug

Select code. Use the action. The selection is already in the prompt. That is the whole trick.

Explain and a few Reviews a day are free. Refactor and Debug are Premium. They are the same muscle: Grok sees the snippet (and, if you have Collections, more of the project).

Use Review when you want a second reader. Use Refactor when you already know it is ugly. Use Debug when the stack trace is lying to you.

Custom action buttons (Premium) are for the prompt you type every week.