i have a 12week old sharpei, she has started going out for walks , but doesn't do the toilet on our walks ,  this is my first dog and i would appreciate some advice. 

She probably doesn't realise that she is allowed to

If she has only been allowed to 'go' in her own garden she won't realise that the big outdoors is also where she is allowed to go. This happens to a lot of pups, so don't worry. When she does eventually 'go' give her a lot of praise, she will get there.

If you could start teaching her to go on command, eg 'busy', when you let her out into the garden you could then use this word when out on your walks. Mine are sort of trained this way ;) Well a young male will 'go' anywhere, won't he? :D