Satchel Charges are remote control bombs plantable on any flat surface. You can place up to 3 and detonate them simultaneously by pressing Grenade (with the ability selected), or individually by interacting with them from a distance. Enemy fire can destroy them, so try not to plant them in obvious places.
Satchel Charges can technically be seen as the Soldier's equivalent of the Engineer's Landmines. Like Landmines, Satchel Charges have a higher explosion range than standard grenades, and can be used as a form of proximity defense.
Unfortunately, Satchel Charges must both be detonated manually and are visible to enemies by default, meaning they are far easier to avoid. Like Landmines, the enemy is also alerted when one is planted.