An Assault Mission Giver is an NPC who offers various Assault missions for a specific area. Signing up for each mission will cost one Imperial Army I.D. Tag. Advanced missions require a particular Mercenary Rank, before they will be offered.
Accumulated Assault Points are area-specific, and can be spent by buying equipment from the corresponding Assault Mission Giver.
For further information, see the Assault entry, or talk with the NPCs.