Each STIGMA slot can store full set of equipment and each STIGMA can be summoned like a magic spell giving you buff with the status of the equipments
lets say you have
STIGMA for WS: with neck piece +10 agi + hand piece +5 AGI = total buff from STIGMA of ws will be +15 AGI which will last for short period of time
this way you wont need to carry alot of equipments and you still benefit from the stats of the gear