An electrical fuse is used to protect your electrics from large currents, to prevent anything from going wrong with your wiring.
The Fuse has a wire inside it that is designed to melt when the electric current passing through it is too high. The wire will melt to the point that it breaks the overall circuit before damage has been caused.
Three types of fuse exist: 3 amp, 5 amp and 13 amp.
Which amp size do I need?
You should choose a fuse that has a higher current than the appliance actually needs.
For example, a 3-amp lamp you should choose a 5-amp fuse, whilst a 10-amp plug will need a 13-amp fuse.