You'll earn this after playing through the prologue.
*** Spoiler - click to reveal ***This mission is pretty straightforward and serves as an introduction to the game. There's a small timed section, but it's not difficult to do, in which the first bomb will be near you and the other four will be up the ramp and along the wall on the other side of the bridge. When dealing with defusing these bombs, take cover and make use of your party to defend you. When you finish Eden Prime. Is then you're first achievement in this game.