Welcome to the forum. If you buy your own router you do have to set it up. The procedure varies between different manufacturers. You have posted this on the broadband board, not fibre. Regardless I suggest that you buy an ADSL/VDSL version that will work on both. The data you need to set one will be found here https://www.plus.net/help/broadband/broadband-connection-settings/
Your budget will determine how good a router you buy but unless you want to get into the geeky options you should look at getting a BT Smarthub 6 from EBay. These go for about £30 new and perform as well as much more expensive devices. You will find the simple setting up instructions on this forum.
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