If you're talking about time, "gerade" and "eben" are used more or less synonymously as "just", or "a moment ago", while "vorhin" might be translated as "a little while ago" Let's say you arrive at a party and are looking for a friend. Your host says: Er ist eben gegangen = Er ist gerade gegangen = He's just left, i.e. a moment before you arrived, you even might have seen him when you were coming in. Er ist vorhin gegangen = He left a little while ago; the implication being that he left, then something else happened (somebody else arrived or left/the music changed/I had a drink/whatever), and then you arrived.

hallo!