Hi Nurul,
Let's say you have vlan 10,20 and 30 and you want to create 3 ssid and assign them accordingly.
1. Firstly make sure that all your APS are connected to a trunk port.
2. Tag / Allow them with vlan 10,20,30.
3. Go to respective ssid >> under advance options >> access vlan >> enter respective vlan 10 or 20 or 30.
Hope this helps.
Ahamed.