If you don't know much, then I suggest you to read lexicannum or 1d4chan wiki (if you are into childish humour). I think that leader of imperial guard doesn't need to know all that much.

The soldiers are recruited from wherever it's neccessary. If the planet lacks any other resources, they can decide to send men as tithes. Because of this, equipment vaaries greatly and can range from medieval peasants in chainmails with lasguns to something like Austrian WW1 soldiers...  It depends on from where the soldiers are (dead world, hive city...) and how they recruited them.

If you want to go with "vanilla" guardsmen, google Cadians.