Most car handbooks and service manuals include a wiring diagram which can be difficult to follow. The colour-coding, however, is a useful guide to tracing wiring.
The fuse box is often located in a cluster of components, as illustrated here. The box is shown with the cover off.
This is called a negative earth system, and when buying an electrical accessory a radio, for example check that it is of a type suitable for your car system. Fitting a radio with the incorrect polarity will damage the set, but most car radios have an external switch for setting the polarity to suit that of the car. Switch to the correct setting before fitting.
However, it is always advisable to check the circuit also, in case a fault in it caused the fuse to blow. For example, failure of an electrical component or damaged insulation on a cable can cause a short circuit, resulting in a sudden massive increase in current.