Modding Help

Hello everyone,
I love learning but don’t always have all the info to move forward. Im trying to do some of my own mods and learning how to mod skins in general. I have done a few before, but for other skins that were set up very different.

I think the first thing I would like to do is ask what the xml file for the sidemenu that slides out on all the views, I would like to add an extra button, but can not for the life of me find where it is located or what that whole menu would be called.

I know that this is basic but Im hoping that you all will be patient while I learn a few of these basics.