Watch Wendel from Level1Techs he has an entire video series on how to configure pfsense.
Lawrence Systems has a good series as well.
The basic concept is
Internet -> Modem -> Pfsense -> Switch -> Devices
But if you already have internet and need to watch videos while setting this up you could do
Internet -> Modem -> Old router -> Pfsense (subnet) -> Devices
It's recommended that you have a basic understanding of TCP/IP before you start replacing everything so get a crash course in networking as well.