g'day Linda,
first up, what is the make/model of the TP-Link router?
next, do you want your PC to be wireless or just have wifi capability in the house for others?
if your PC doesn't need to be wifi, leave it connected via the ethernet cable to the original modem as it was.
since you mention other wireless capable devices in the house are connecting to the internet then the new router must be configured OK.
I assume you logged onto its configuration menu via a browser and set that up (?).
as to cabling, there will be an ethernet cable to connect the router to the modem and another to connect your PC to the router (if you want to stay hard wired).
when you bought the new router, they usually come with a nice little diagram on on to do that.
if you want to go wireless, your PC will either need a wifi adpater (either an internal card or a USB wifi stick) or if it already has one, it'll need to be setup to join the new wireless network.