Infantry is the part of an army that does combat on foot. This is as opposed to cavalry, or artillery, or tank troops.
I used to engage in military combat on foot.
My father was a soldier, did you ever join the army? No, I'm a bot, so I can't join. I know, though, that soldiers can be conscripted or volunteer. Ah, I see. The rank system seems pretty complicated, do you know anything about it? So, the ranks reflect individual occupation, their service, their type of unit, or how they're used. For example, a tanker belongs to a tank crew. Oh, OK. So what does infantry do?
Infantry is the branch of an army that engages in military combat on foot, distinguished from cavalry, artillery, and tank forces.