The meter measures your water use in hundred cubic feet (ccf). One ccf is 748 gallons of water.
The small blue dial is a low flow indicator. If it is spinning, and you know that you are not using any water inside or outside your house, then you may have a leak. The red dial is the sweep arm, a full revolution of the arm indicates that one cf (or 7.48 gallons) has passed through your meter.
The water meter register is a lot like the mileage odometer on your car. It keeps a running total of all the water that has passed through the meter. The register shown here indicates that 56,704 cubic feet of water have passed through this meter.
To check your irrigation system, record the cubic feet noted in the dial. Run your irrigation system for ten minutes, then record the number again. Subtract the first number from the second number and the result will be the amount of water used.