Wireless AP for internet connection

Hello,
I would like to setup my NetMetal 5 routerboard (RB922UAGS-5HPacD-NM) to provide wireless access point and internet connection to different device of our office (laptop, smartphone).
Internet connection is provided by a router.
Router and NetMetal 5 are into the same local network (simple switches, no firewall in the middle).

Can you help me?
I have read wiki and some guide but nothing…

Thanks in advance
Andrea