What does "Clean All" do?

I have been tasked (as a junior developer) with doing code reviews on old hacked together C# code written over the course of the past couple years in MonoDevelop.

I am moderately familiar with MonoDevelop, but the Build > Clean option… I just can’t find any documentation on it.

I’ve hit the button… and it shows it’s thinking about something for a moment, then… as far as I can tell… nothing at all happens.

Can you point me towards a resource, or tell me (in whatever level of detail you are comfortable with) what it actually does?

Clean will remove the build artifacts from the previous build. If there are any other files in the build target directories (bin and obj) they may not be removed, but actual build artifacts are.