I've been watching how-to videos and some say to put on a pwder to set the foundation (I guess it's for liquid ones only?). what is that powder they're talking about? is it just another powder foundation they're using? or is it something completely different then what I'm thinking?

they are called translucent powder.
loose powders that effectively stabilize and fix makeup. Micronized pigments and talc render color purity and an ultra silky, soft feeling application. The finish is velvety matte and the coverage is sheer-light. The range is unique, encompassing colourless to complexion-enhancing, colour-balancing shades. you can get them at MAC

That is called a translucent powder you can get them pretty much any wear every carriesrrys them i use them 2 set all kinds of foundation and you can use it if u have a fair complextion but u have 2 use it lightly or it will look pale

Oh if u like how 2 videos u should cheack out enkoremakeup eyelovemac TheLookForTeens Pursebuzz dancer4life34 and luckyprettyeyes at youtube.com i hope i helped

Oh you mean compact powder ?
It's so the foundation stays on and doesn't look shiny !
=)