Fortinet Firewall, Mikrotik router

Hello

I've got the following set up and need some advice on filtering my traffic through a Fortinet 200 router/firewall. I'm way out of my comfort zone on this, but I'm stuck with trying to fix this until my new guy starts.

I can follow instructions and have some basic knowledge of networks, but still treat me ike an idiot.

We have a router from ISP currently connected to a Mikrotik router which connects to a cicso managed switch.

All my traffic should be filtered by our Fortinet200, it appears that our IT guy (who bailed after being found to be less than effective) decided to not route traffic through the fortinet and basically give free access to the internet to all.

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We were using a fortinet in the past, I can't remember though if it was prior to the network upgrade or not. So I dont know if at any point the new 200 Fortinet as been used or not.

Is there a simple way to place the Fortinet between the mikrotik router and the WAN and let it just filter everything for the time being until my new guy arrives?

I don't care if it is rough and ready, as long as it is filtering properly. I know it cant be as simple as just plug it in and set a WAN and LAN side to the fortinet but I'm hoping there is something close to this.

We used to have individual logins for the network, that all appears to have stopped other than the wifi which remains and is through the mikrotik router as well.

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Thanks in advance