AGI increases your power, since you're a scout.
STA increases hitpoints.
STR increases damage...I'm not entirely sure how...I'm thinking maybe allows you to hit for the max damage more of the time. Like if your weapon says 20-30 damage, you hit for 30 more often. Could be wrong though. Also, of course, it increases how much you can carry.
INT and WIS currently have no effect for a ranger, though I've heard that they may make them useful later.