ASI
The Air Speed Indicator is much like the speedo in a car, it tells you how fast you are going. However, whereas a car's speedo shows how fast you are traveling across the ground, the ASI shows how fast you are moving through the air, not necessarily the same thing. Consider a glider flying at 55 knots (shown on the ASI) into a head wind of 15 knots, the seed of the glider across the ground would only be 40 knots.
Altimeter
The Altimeter shows how high the glider is. It can be set to show the hight relative to the aifield, sea level, or any other point. The long hand shows hundreds of feet, the small hand thousands of feet and the arrow tens of thousands of feet, so the altimeter in the picture is showing 200 feet.
Vario
The Vario shows whether the glider is going up or going down. If the needle is above zero the glider is climbing, if the needle is below zero the glider is sinking. The scale shows how fast the glider is going up or down in knots. So, the vario in the picture is showing a climb of 2 knots, or 200 ft per minute.
