The Fullerton Amtrak Station will probably always be one of my favorite starting points. The colonial meets early California bungalow architecture blends in with the area and reflects a calmer time when Fullerton was actually a town surrounded by orange groves and ranches. The station serves both Metrolink and Amtrak. Metrolink tickets are purchased outside from a machine, Amtrak tickets are purchased inside at the window. (This may change in the future.) Train employees are friendly, knowledgeable and ready to help it needed. If going south (or east), climb the stairs and take the bridge to the other side of the tracks. The snack bar isn't much to speak of, but the retired train guys who meet there in the morning sometimes for coffee just give the depot more atmosphere.
Fullerton prides itself on free parking, but depending on the time of day, you may have to park in the multi-storied parking garage. Again, read the signs and follow directions because things change.
Everyone should take a train trip at least once, even if it's only to a destination an hour away, before we lose the chance completely.