Its a big subject but here's a start. I'm assuming XP or 2003 version

Yes you use masters in PPoint - in fact they're vital! Masters lead to
presentations with slides with a common style and also allow logos, footers,
graphics etc to appear on all slides

The Master slide controls the font, font size & colour and the position of
titles and text placeholders. Also any graphic that you want on all slides
should be on the master.

The master is also where you can set a common background either solid
colour, gradients, textures or pictures.

Heres the confusing bit each master can have just a slide master or both a
slide master and a title master. Most downloaded templates will have both but
the default if you design your own is just a slide master.

If there are both the title master determines tha layout etc of slides with
title slide layout (normally slide 1) only and the slide master determines
the layout of all other slides.

If you have just a slide master it automatically changes the (invisible)
title master to have the same font styles, graphics and background etc so the
whole presentation has a common theme.