Hitting the ball:
Select the AIM button by scrolling to it (up/down), then clicking FIRE.  The red line is your aimer and can be moved with left/right/up/down.  FIRE confirms your aim.  Next, select the ball contact height by pressing up or down, then click FIRE.  A lower contact height gives the ball more loft and possibly more distance, but also causes it to fly higher, which increases the wind's effect.  A higher contact height has the exact opposite effect.

Click the CLUB button and select a club by scrolling and clicking.
The club's TOTAL SHOT LENGTH and name are shown on the club-face in the bottom left corner of the screen.
The TOTAL SHOT LENGTH includes the ball's initial flight plus any bouncing and rolling.
Hitting an over-powered shot or landing off the fairway will affect the distance the ball travels.

The swing meter shows your swing power and accuracy.  Click the SWING button to set the swing meter into motion.  When the meter reaches the desired power level, click to select your power and start the downswing.  The green region near the left hand side of the swing meter is the ACCURACY REGION.  In order to hit the ball correctly, try to click the wheel when the meter's indicator is in the center of the ACCURACY REGION.  If you click to the left or right side of the center of the ACCURACY REGION, your shot will curve in that direction.  The degree of your shot's curve is affected by how much you missed the ACCURACY REGION by.  Note:  the ruled area between the ACCURACY REGION and the red line, inclusive, represents the shot's power from 0 to 100%, with each white line representing 10%.  If you select a shot power to the left of the ACCURACY REGION, it won't go anywhere at all (it might fall off the tee though).  It is also worth knowing that the swing meter indicator descends faster on more powerful shots.

Practice swings:
After clicking to initiate the swing meter's movement, if you don't click again until after the swing meter finishes moving, you will not be penalized by any strokes.  This can be useful for getting a feel for the swing meter's movement.

The red line on the swing meter is your max power.  Shots can be made with extra power by clicking to the right of the red line during the upswing, but over-powered shots will be less accurate.

Putting:
Putting requires that you select the appropriate power to get the ball to roll slowly over the hole.  If your putt crosses the hole too quickly, it will not sink.  The putting stroke requires that you select the shot's power, but not accuracy.

Terrain:
Different types of terrain will affect your shot power and accuracy, making it important to pick the right club for the job.  Basically, the longer the grass is, the less accurate your shots will be (and the more power your shot will lose).  Hitting off the rocks is difficult.  Short clubs are more forgiving than long ones.  If you're in a sand-trap, you should use the sand-wedge because it's perfectly suited to the sand.  It's also worth noting that the driver is only accurate when shooting from the tee.

Many factors will affect a shot's accuracy.
-Shot power: lighter shots are more accurate, over-powered shots are less accurate
-Picking the wrong club for the terrain (eg: the driver is inaccurate if the ball is not on the tee).  Some terrains will affect accuracy regardless of club selection (eg: a rocky shore)
-Club length: shorter clubs are generally more accurate (the sand wedge should only be used in the sand though)
-Wind

Factors that affect a ball's range:
-Shot power from the swing meter
-Terrain under the ball when swinging (long grass, sand, and rock reduce swing power)
-Terrain under the ball when bouncing and rolling (eg: sand reduces bounce, while the green increases roll distance)
-Selected club 

Good luck!
