"A partir de" se utiliza para expresar que desde un determinado momento en adelante se llevará a cabo cierta acción o acciones. Ejemplo: A partir de mañana dejaré de fumar y beber.

Hi, I'm mexican and we use that phrase before we want to add a reference to someone's idea. A partir de la definición anterior... Also if you are giving directions and you are explaining after one point to other. A partir de ( Gas station) walk two bloks east.

I'll reply in English, I also had this confusion. Maria's and Julio's examples are great. Used with an adverb of time, "a partir de ___" means "from ___ on" or "from ___ going forward". It also has the meaning of "since" in the time context. Confusingly for us English speakers, "a partir de ahí" means "since then" (apparently "ahí" can also mean "then"). And confusingly, "a partir de aquí" also refers to time (from now on) not location. Lastly, I ran into "a partir de la mala información" in a news article a couple of weeks ago, it means "based on bad information".

You could translate "A partir de ahora" as "hereinafter" so "A partir de " is always connected with an specific time period (i.e: hour, day, month, year.... now, tomorrow)

A partir de... quiere decir que desde ese momento en adelante harás determinada acción o sucedera algo... A partir de hoy empiezo la dieta / A partir de la semana que viene no como mas carne. A partir de mañana comienza el invierno / A partir de mañana se entregarán los uniformes