A Newbie and a Wannbe

I am new to blog development so don’t shoot me for asking what may seem like a silly question 😉 I only know CSS and HTML…. but I am hoping I can make enough connections with code, common sense and forums to do what I want.

I am modifying a theme and want to change the navigation titles as well as add to them. This theme ‘modmat’ is based off of Sandbox.
For the life of me I don’t see where I can do this. I have adjusted what I could with the /* MENU */ and I see that <?php sandbox_globalnav() ?> is referenced in the PHP but for the life of me I cannot find code with the word ‘About’ that may clue me in to what I need to do.

I was thinking somewhere in functions/sandbox.php or modmat.php or just functions.php………. ANY HELP would be GREATLY APPRECIATED.