while watching baseball, i sometimes hear that the opposing manager will challenge a switch hitter and make him hit from the other side of the plate, is this true. if so, what exactly do the rules imply?

There are no rules governing switch hitting. What most likely they are referring too is that the manager will bring in a pitcher that throws opposite the current pitcher. The idea of succesful switch-hitting is that it is easier for a right-handed hitter to hit a lefty pitcher and vice-versa. Most switch-hitters though do have a weaker side so sometime a manager will see that a switch hitter is worse batting right or left handed and bring in a pitcher opposite that and cause him to switch sides and hit so he's still opposite. No rules involved just tactics

They're not actually making him hit from the other side. Switch hitters normally bat righty when facing lefty pitchers and lefty when facing righty pitchers. This allows the batter to see the breaking pitches better. Lets say for example that a switch hitter hits better from the left side of the plate. The manager will bring in a lefty pitcher, "forcing" the batter to hit from the right side.