Joining two different network interfaces together

Hello everyone, I’m using RouterBoard RB951ui-2hnD to access two different networks A and B. A network which is 192.x.x.x is for my internet connection and the B network 100.x.x.x is for my server. Can someone please explain to me how to access both networks using my router. P.s I’m new to mikrotik brands

Thanks

Read all the literature first.
If you dont understand anything suggest returning the unit and buying a linksys.
So far I see no effort on your part to do some of the work.

Start here.
https://help.mikrotik.com/docs/