The digital switchover refers to the date when the old analogue transmitters will be switched off in your area. People who've not got a Freeview set-top box, or a TV with Freeview built in, will no longer be able to watch TV.
But those who've already 'gone digital' won't notice any changes (except that those people who've experienced occasional picture break-up with digital reception will probably find that the problem has been fixed, because the digital transmitters will have been turned up to full power).
Chris