Hi i have a remote key for my fiat grande punto but i need a code to programme it to my car ???

It's not a DIY job and needs specialist equipment.

Take the car along with ALL remote keys to a Fiat main dealer. Any keys you do not take along will not work afterwards. Fiat can then program the vehicle and remotes as a matching set.

Note that it's worth shopping around for this: it doesn't take much time or labour so there's likely to be a wide variation in pricing. You can also try asking independent automotive locksmiths whether they can provide the service: many can these days but there are also plenty who haven't invested in the technology needed to do the job.