Hi,
Forgive the dumb question but there seems to be information overload on VLAN’s in the Mikrotik world and I can’t see the wood for the trees 
I have a powerbox pro (hex POE), and need to configure two of the ports to be VLAN access ports? I can see it needs to be done in the Switch menu but not sure which is the easiest way?
ether1 - link to router
ether2 = VLAN 90
ether3 = VLAN 91
Any help would be appreciated.
If you follow VLAN switching manual (the Other devices with built-in switch chip part), you should be able to get it done. And this would be the most device-friendly way.
It might be easier to implement functionality using bridge vlan filtering stuff (as described in this fine tutorial) and in your particular case you might even not loose any performance. Otherwise this way is not recommended to use on majority of device types because this way all the traffic is handled by device’s (relatively slow) CPU.