Confusion on vlans regarding wifi

Hello,

I am trying out routeros and found this https://www.marthur.com/networking/mikrotik-setup-guest-vlan-wifi/2582/ guide on how to set up a guest wifi.

Why do I need to add a bridge and why do I need to add the VLAN interface to the bridge if I create it under the interface of the virtual wifi?

Hope someone can clear this up for me.
Kind regards

Ignore youtube, for your own sanity LOL.
Here is the current standard on using vlans…
Works for wired and wireless as you will see.
http://forum.mikrotik.com/t/using-routeros-to-vlan-your-network/126489/1

Thank you as I thought people just pick some configuration up and repost it while the config doesn’t even make sense