hi, apologies for the basic way i'm going to explain this - i know absolutely nothing about maya or 3d

i'm trying to catch up on the first lesson i missed in class while the tutor is away.

i had to set up reference pictures on poly planes. after spending two days trying to work out how to fit the image to the plane... i've managed it.
the next thing done in the lesson, was the planes were moved out of the way of the central grid in perspective view, giving a clear view, but still visible in the hoto views... done that... but how do i lock those planes so i dont keep selecting them? i know this is a very simple question, but i don't think i have the energy to spend another two days trying to find out the hard way...

also, the tutor mentioned something about working on just one side of the model -- whats the best way of doing this?

thanks in advance