Whats what, and do I need it? if so... why.

The main purpose of a rain gutter is to protect a building's foundation by channeling water away from its base. They also help to reduce erosion, prevent leaks in basements and crawlspaces,protect painted surfaces by reducing exposure to water, and provide a means to collect rainwater for later use.

The facia board extends around the building just below the roof line.
As well as making the building more aesthetically pleasing it covers up the roofing joints and can help prevent damp and corrosion.