How to use RouterBoard RB450 as Firewall?

Hello,
I never use RouterOS before and need help to setup RB450 router as Firewall device. I am actually don’t need any router or any other futures of device, only Firewall. I have 2 local networks connected to each other and company want use RB450 as Firewall between networks (I know there are many other devices for that but it must be RB450 only). Is it possible to disable all ports and connections between two networks and tell firewall use only two IP?
For example PC1 ip 10.70.8.106 PC2 ip 10.70.8.14
only these two IP must communicate between each other, everything else must be rejected. Any other IP on network must be completely rejected by Firewall.
Any help how to setup Firewall filter rules or other settings? It must be simple basic script I just completely new to this. Any help will be appreciated!