Not sure if I clearly understand what you are asking. In general, Infantry's role is to "close with and destroy" the enemy with armor support and in this specific case of combined arms operations. It is the infantry that holds the ground, so whether the infantry moves on foot or in APCs/IFVs with the armor, the idea is to get infantry in the vicinity of contact with the adversary and then through superior fire and maneuver, assault and take over the positions (you could add 10 other missions/capabilities to this list that the infantry could deliver on).
How the infantry is employed when the armor moves depends on the situation and the frontage requiring coverage. There are entire manuals written on infantry employment with combined arms as well as on the movement to contact. You are essentially teaching both infantry and armor to advance while keeping in mind own and opposing direct/indirect fire among a thousand other considerations.
