I hope that you have an RCD either in the house consumer unit or in the garage that provides safety protection for this spur to the garage?
If not your first priority will be to get one installed!
If you have a spur from the ring then you can only have one socket on it. If you were to terminate the spur in a 13A fused spur (FCU) then you can run as many sockets as you like from the output side of the FCU but be aware that the total max load on all of those sockets will be 13A.
Do please remember that there is legislation governing electrical work like the one you are contemplating....