If the router is wireless, they can both connect to the same router. Wired and wireless connections to the same router are the exact same connection, just different methods. As to how, depends on your setup, the router manual will explain how to setup wireless and connect devices to it.
" Can I have my PC plugged into the router whilst having my laptop wireless? "
If this is how it's currently setup, it should just work.
You can have up to 4 PCs connected to the router (depends) via cable and plenty of other devices connected to it wirelessly. That's what a router is for.