davideboracay,
As shown in the picture, the control arm is mounted on the servo at it's center point. A line is attached to each 'end' of the arm, one running to the foresail, the other to the mainsail attachment points through a hole in the deck (it's all mounted inside/under the deck). At full travel in one direction the servo pulls the sail in 'tight' (straight fore/aft), at full travel in the other direction the sails are full 'out' (90 degrees with the centerline of the boat, maybe).
The amount of 'travel' depends on the length of the servo's control 'arm', where the lines are connected to the 'arm', and also where they are connected to the sail/boom. Need less 'travel' on one sail than the other? Move that line's attachment point closer to the 'arms' center (slightly). Need lots of 'travel'? Attach the line to the end of the 'arm'. Lots of variation available.
The 'biggy' is that the servo be strong enough overcome the pressure of the wind on the sail. The more area of the sail and strength of the wind, the larger the servo. The stiffness/strength of the servo arm should be such that it doesn't flex when in use (or at least not very much ).
From there, it's just a matter of adjusting everything to suit your boat. Good luck!
- 'Doc

Oh, linning the 'hole' through the deck for the control lines with something to keep from making the lines snag/fray is a good idea too (metal grommet, as in shoe laces?).