What is the difference in usage between 'Por' and 'Para'?

Por is used to talk about movement, modes and means of travel and communication, exchanges, duration, and motivation...

Viajé por Francia y España = I travelled through France and Spain
Te cambio mi manzana por tu fresa = I will exchange my apple for your strawberry
Tengo que trabajar por ocho horas hoy = I have to work for 8 hours today
Trabajo por ti, porque te quiero cuidar. = I work for you, because I want to take care of you

Para is used to talk about destinations, recipients, deadlines, and goals.

Salgo para Chile mañana = I leave for Chile tomorrow
Este regalo es para Adela = This gift is for Adela
Necesito la presentación para el viernes = I need the presentation for Friday
Trabaja mucho para ganar más dinero = I work a lot to earn more money