This where it gets tricky.
You have to make the network at your office “see” the network where the core is and vice versa.
If the Core cannot see the devices at the office, you cannot use them as endpoints.
So if you have no networking experience this is going to be tricky.
But when you search “VPN” on the forum you will find that some have succeeded and failed and all in between.
This means you have to have knowledge, equipment and the means to test you specific solution.