A GFCI outlet is designed to protect you from electric shock by quickly cutting off power when it detects a ground fault or an unintended electrical path to the ground. Similarly, a GFCI breaker serves the same purpose but is installed in your electrical panel.
Whether you will need one or both systems depends on your specific situation and the level of protection you need:
In most home settings, choosing one form of GFCI protection should keep your electrical systems safe.