Careful with this very common mistake! It may not seem like it will make a big difference, but it can, in fact completely change the meaning of what you are saying. Por is used for: 1) travel and communication (vamos a hablar por Skype / viajé por España); 2) duration (miré la tele por ocho horas); 3) Motivation/reason to do something (estoy aquí por amor); 4) to indicate a period of time: por la mañana, por la tarde Para is used for: 1) destination (este tran va para Londres); 2) something is destined for someone (este regalo es para ti) 4) Goals - careful, this is different than motivation (estoy aquí para ayudarte) 5) deadlines (tengo que terminar todo eso para Viernes por la tarde)