Just follow the official documentation on this:
https://help.mikrotik.com/docs/spaces/ROS/pages/224559120/WiFi#WiFi-CAPsMAN-CAPVLANconfigurationexample:
And in regards to basic VLAN information, there is a great topic:
http://forum.mikrotik.com/t/using-routeros-to-vlan-your-network/126489/1