Basically a fiber cable uses glass to allow light signals to pass through. Unlike copper cable which uses electrical impulses a light signal source is used. The light signal passes over a greater distance than copper before requiring the light source being boosted. Each end of the cable uses a media converter to change it from light to electrical impulses.
Fiber comes in two mediums they are single-mode and multi-mode. Multi-mode has a distance limitation, approximately 600 meters before it needs to be boosted. Single-mode can travel up to several hundred kilometers before its signal needs boosting.
Unlike copper fiber is immune to lighting strikes or electromotive forces (emf) generated from other sources. Fiber requires vigilance when installing. Because it's glass, it must be installed so that any bends in the cable do not interfere with the light that passes through it.
Fiber is more costly than copper wiring but in many cases the higher speeds offset the cost to install and maintain.