How does Rageblood Shaman's ability work?
This ability is a static ability. The important rules from that page say


  
  604.1. Static abilities do something all the time rather than being activated or triggered. They are written as statements, and they're simply true.
  604.2. Static abilities create continuous effects, some of which are prevention effects or replacement effects. These effects are active as long as the permanent with the ability remains on the battlefield and has the ability, or as long as the object with the ability remains in the appropriate zone, as described in rule 112.6.
  


From the first rule, Minotaurs "getting" +1/+1 isn't an event that happens (and definitely not repeatedly), it's just stating a fact: that each other Minotaur has one more power and toughness than it would otherwise.

Regarding continuous effects, the rules say


  
  611.3a A continuous effect generated by a static ability isn’t "locked in"; it applies at any given moment to whatever its text indicates.
  611.3b The effect applies at all times that the permanent generating it is on the battlefield or the object generating it is in the appropriate zone.
  


Basically, any time Rageblood Shaman and another Minotaur are on the battlefield, that Minotaur gets +1/+1 and trample. It doesn't matter which entered first, and it only works when the Shaman is on the battlefield.