Squad Commands are a specialized gameplay mechanic that appears in Spec Ops: The Line, which adds a sense of tactical thinking to the gameplay.
By holding down "RB" on Xbox, "R1" on PS3, and "F" (by Default) on PC, and releasing it over a highlighted enemy, Walker can mark priority targets for his squad. Adams and Lugo will then concentrate their fire on the highlighted target until it is killed by them or by Walker.
There are also other situations that Walker's squadmates can perform special actions depending on who attacks:
Adams lobs grenades into groups of enemies, or entrenched enemies, and Lugo uses his sniper rifle to take out enemies that are at long range, such as snipers.
Lastly, if the squad sees Walker is suppressed by heavy fire, a prompt will appear on-screen for the "Stun Command". Tapping the Command button will make Adams and Lugo throw a flashbang at the group of enemies, leaving them stunned, and enabling Walker to escape from tight situations.