The spell determines the single most basic function of each magic item, including how to activate that function (if appropriate), and how many charges are left (if any). For a weapon, this will be the "plus" to attack and damage.
If a magic item has multiple different functions that are equally basic, identify determines the lowest-level function. If these functions are also of equal level, the DM decides randomly which is identified.
Arcane Material Components: Worth at least 100 gp value.