UNIX for Advanced & Expert Users

My understanding is when you see a man page command with a (3), is that this is a library call such as XSetScreenSaver(3) .. Sometimes these "calls" seem to do exactly what I need from a command. is there a way to access these calls from the terminal and just run them like a normal binary? How are they normally used? Are they just called from a C routine as some library to add functionality to programming?

Actually, many do have command equivalents - try an "apropos" to find them - or sometimes even a "man -a whatever"

But if not, then yes, they'd be called from a program. If you have no idea how to write a simple program (and for many things, it would be simple), see my Writing and Compiling C programs on Linux which will at least get you beyond the "Huh?" stage.