3 numbers on bottom are combat strength, ambush strength, and movement. Most units have 20 MPs, Cav has 30, militia have 10. Cornwallis is a 4 init, most are 3. Many units, esp. The ambush number must be circled to use it offensively.
Ambushes can only take place in wilderness hexes.
Indians have ambush but not much regular combat ability. For normal combat strength if boxed, it is halved on attack, most US are boxed. Militia show up in the appropriate state and can move away, but they get to show up dynamically if not already in play. BTW, both BR and US have militia. There is reaction movement so a general's initiative is crucial to move or react move, pick up troops not originally stacked with the gen'l, and continue a combat to decisiveness, etc.