How are the two buttons that execute code different?

On the left-hand side, there are two buttons, an arrow and a cercle:


So far I have not been able to figure out how they are different. I initially assumed the arrow would just execute the code currently selected, and the circle would execute the whole script, but this does not seem to be the case.

In that frame:

- Would it be possible to add tooltips on the buttons to clarify what they do?
- Would it be possible to run only the selected code with the triangle? I find the ability to just edit-and-run small pieces of code in a script very helpful in exploring / understanding what is happening.