1. PGF
   Pressure Gradient Force (PGF) is the initial force that causes air to move. PGF is represented by an arrow indicating the direction of air movement. Air will ALWAYS begin to move DIRECTLY AWAY FROM HIGHER PRESSURE and DIRECTLY TOWARD LOWER PRESSURE in order for the atmosphere to achieve a pressure balance. Keep in mind that the final wind direction will NOT be along the PGF in most circumstances. (Exceptions include small-scale flow such as a sea-breeze or a tiny gust of wind, etc.)

2. Coriolis Effect (Force)
   Once the air begins to move along the PGF, a second "apparent" force called the Coriolis Effect or Coriolis Force (CF) causes the air to deflect from its initial path. In the northern hemisphere, the CF-induced deflection is 90^o to the right of the intended path. In the southern hemisphere, the CF-induced deflection is 90^o to the left of the intended path. The Coriolis Force is caused by the rotation of the earth.
   (View this example multimedia file [1 Mb])

   As with any force that causes an object to be displaced (moved), the amount of displacement will be a function of the time that that force has been exerted on the object. At zero time, there would be no movement due to the force. As time increases, there would be a more noticeable displacement. The Coriolis force is a VERY WEAK force so it takes a fairly long time for one to notice its effects!

   Therefore, the Coriolis Effect only occurs when a freely moving object travels a large distance (i.e. travels a long time.) An example would be air that is moving over hundreds of miles which takes many hours to do. Contrary to public belief, water draining in a sink is NOT affected by CF because there is not enough time for the Coriolis force to cause a noticeable displacement. Read the TRUTH ABOUT CORIOLIS

   When PGF and CF act upon an air parcel, the resulting wind direction will be parallel to drawn isobars with lower isobars to the left of the wind in the northern hemisphere. Another way to imagine the wind in relation to pressure is to place one's back to the wind, sticking out the left arm. The left arm would point to lower pressure in the northern hemisphere.

   Because flow is parallel to isobars, air around the center of a high pressure system in the northern hemisphere flows clockwise. Air around the center of a low pressure system in the northern hemisphere flows counter-clockwise. Direction of flow is reversed in the southern hemisphere since CF acts to the left of the wind.

   If just PGF and CF are considered, air from a high pressure region can not move toward a low pressure region, thereby not allowing the atmospheric pressure to balance. It takes friction at the surface of the earth to achieve this pressure balance.

3. Friction
   As air moves along the earth's surface, frictional forces reduce the wind speed. Coriolis Effect is a function of latitude and wind speed, so slower winds caused by friction REDUCE THE CORIOLIS DEFLECTION. Instead of the air being deflected 90^o to the right of the PGF in the northern hemisphere, the wind will end up flowing about 60^o to the right of the PGF.

   Since air flow is NOT parallel to isobars but instead is moving slightly toward lower isobars, pressure balance between high and low pressure can be achieved. High pressure - air moves around clockwise and away from the center. Low pressure - air moves around counter-clockwise and toward the center.

4. Global Wind Circulation
   The lab is pretty clear about this so I will not repeat it or myself. The best help I can give you is to tell you that you should be able to completely reproduce the illustration used in IAS Question #6. Understand where high and low pressure regions are, where air is either rising or sinking, where it is wet vs. dry, and the surface wind flow between each 30 degree latitude region.

Helpful Links:

Forces & Wind - MUST SEE!
Coriolis & Fired Rocket Example
Global Winds & Hadley Cell
Global Winds & Hadley Cell #2
Global Wind Patterns
Wind Chill Chart