Any advise please
15 week old staffy bitch refuses to walk on lead out of the garden? she will happily walk within the garden. but if we take her outside the garden she sits down sometimes even lying. we've tried gently tucking her but she still refuses to move. 

She is probably overwhelmed by the outsie world, let ehr just sit or lie there until she wants to move.  Always walk on the side of the road so that traffic is approaching head on and not from behind.  As soon as she gets uo then encourage her to you with a happy voice or even treats.

Please don't pull her along as this will frighten and overwhelm her even more.

You could try picking her up, leaving the garden gate open and gently placing on the floor about 3 feet away from the gate on her lead. Hopefully she will want to go back to the safety of her garden and head back. Make a big fuss and tell her what a good girls she is. Practise this a few times a day and she should start to gain in confidence so you can increase the distance.

I agree with both posts have you tried carrying her around the shops getting her used to the hussle and bustle of life, even try some training classes there great for socialisation.  Good luck susan