In iTunes, what does "organize library" and "consolidate" do?"

Recently I had to reformat and reinstall my Mac OS. (10.11.6. El Capitan -- the highest my mid 2007 machine will tolerate). On my old setup, over a matter of 13 years, my music files became scattered and embedded throughout the system. What I want to do is get and keep my iTunes music and library cleaned up and in one location. In doing so, I'd like to know exactly what "organize library" & "consolidate" does. I thought I knew this at one time. But, I've had several "Senior Moments" since. Now, due to COVID-19 constrained isolation, I seem to have time to putz around with my older, faithful MAC, which will need replacing sooner than later.