Hi. Im quite new to routeros.
I have read most of "routeros by example" and now I would like to set up the AP for the router and I don't have a clue.
I would just need basic functionality.
my hardware is rb3011 and a unifi ap ac light.
Thanks.

Assuming that you already have RB 3011 operating as your local gateway:
1. You set-up the controller to a pc.
2. You connect the unifi ap to lan, it gets a local ip lease from dhcp
3. you ssh to unifi ap and set the inform url
(or you set the inform url as a dhcp option on the dhcp server).
4. You use the controller to further setup the ap.

Alternatively, you can use the discovery util.
Also have a look at https://help.ubnt.com/hc/en-us/articles ... management, it explains the stuff.