I own a Bush 14" Portable TV (and I dont need to tune in the channels as I have got Sky) and this is the method that I used when we didnt have Sky.
1. Plug in a portable or outdoor aerial.
2. Go to the menu on your TV.Then go to CH (or Channel) Tuning and search for signals. (Note: If it is a crap signal, ignore it and see if you can get better one. If the signal is really crap the TV will usually ignore it.)
Hope this had helped