stupid question, but have to ask? growbox fans?

what does it mean when peeps say intake and outtake fan for a grow box? passive or active? and how does this work, is it just one fan blowing into the box and one faced blowing out and if so how does the outake suck in air to blow out, do fans create suction behind them when running?

unless you get a magic, air creating fan, the fan has to pull the air from somewhere. It does suck from one end, and blow out the other end.