To protect the components in the circuit from overcurrents.
The cover of the fuse block will have the diagram for the circuits.
A fuse.
horn Gap fuse, used in 11kV & 33kV circuits to disconnect in case of fault.
Yes, all circuits are protected by a fuse.
No, they are separate circuits.
Circut Breaker
No, they are on seperate circuits.
to many plugs in at once or old circuits ECT.
The fuse for the horn and other circuits are located just a little left of the clutch pedal.
No such thing as a relay fuse, you have a fuse in the wiring for each circuit, and some circuits also have a relay to reduce the amperage on a switch. What is not working on your car? then look up handbook supplied to find the fuse location in fuse box for the thing that doesnt work. if fuse ok then check relay but this needs more experienced person to do.
Circuit breakers. Some older homes still have fuse boxes.
All circuits must be protected by a fuse. Your vehicle handbook should tell where to find it.