You cant "make" your TV digital, but you can plug in a Freeview box which can pickup digital signals and you can watch them on our TV.
So the answer to your first question is you need a FREEVIEW box.
This normally plugs into a SCART socket in the back of your TV.
A video recorder and a DVD player also usually need a scart socket to plug into your TV, but I doubt your TV has 3 scart sockets.
You can buty a device from places like Argos which allow you to plug 3 scart devices into a single box, and then use one plug into the TV.
Then you can switch between whatever device you want to use (freeview, VHS, DVD)