You first need to decide whether it is worth fixing, or not.
Just about everything on the bike can be brought back into service, or replaced, but the cost could be more than getting a good, replacement bike.
More important, of course, you need to be safe.
It is hard to provide useful, general guidance about whether a bike is serviceable, or not. We might be able to help if you get in touch at email@example.com. Some photos might help. You might also consider a trip to the Portsmouth Cycle Centre – a local group of volunteers prepared to help you with bike maintenance.
On the other hand, if all your bike needs is some attention, we provide advice for looking after your bike here. We cover using a specialist bike shop and describe ways to ‘do it yourself’.