What are the roles of an Infantry and Guard Division?

Question

I mean how do modern warfare go about with the airforce, combat engineer, scouts, commando units go hand in hand?

Answer 1

No infantry doesn't mean "hand to hand". The infantry is the ground soldier .. aka the "grunt". Meaning they do the grunt work. Guard duty, securing perimiters, patrols, conductiong missions usually on the ground with the assistance of many support units. Picture the Infantry like a soldier in vietnam walking around the jungle doing patrols often times being in the bush for extended periods of time.
As far as combat Engineers go they are usually a group of highly trained soldiers who are attached to infantry divisions and are called in to clear mines, blow bridges, remove obstacles ...ect. They go hand and hand with the infantry to complete the mission.
The "scouts" as you call them really don't exist in the modern military. The closest your gonna get to a scout are Recon units and pathfinder units that are Infantry as well although they go to specific schools for this type of training. Mostly they serve right with the general infantry soldier.
The airforce is just that the airforce. Their missions are for air supperiority and help the infantry and military by bombing and keeping the air secure. The modern military is a pretty complex process and when it is working well preforms brilliantly,