Learn the basics of how an abacus works online at a website or offline with an physical abacus. This instrument consists of a frame holding several vertical bars, which carry 7 beads. The lower part of the abacus is divided by the upper part by a horizontal bar. There are 5 beads on each vertical bar at the lower part of the abacus. These beads are the earth beads. Each of these beads has a value of 1. The two beads in the upper part of the abacus each have a value of five. These are the heaven beads. Additionally, each vertical bar represents a place. From right to left, the place represented by the bars are the 1s, 10s, 100s, 1,000s, 10,000s place, and so on. Thus, the right-most bar represents the 1s place, the one next to that the 10s place, and so on.
Start with the bar representing the 1s place when adding or subtracting. If you want to add 5 + 0, this is shown by moving one of the top beads downward toward the dividing bar. To perform the calculation 5 + 7, move two of the earth beads in the 1s position upward toward the dividing bar. Then move one earth bead in the 10s place downward toward the dividing bar. The resulting number made is 12.
Subtract using an abacus by moving beads in a similar manner as when you were adding. To perform the operation 5 - 1, move the top heaven bead upward and 4 earth beads in the ones place upward toward the dividing bar. This gives you the number 4. To perform the operation, 100 - 7, move 1 earth bead in the 100s column downward away from the dividing bar and move one heaven bead in the 10s column downward. Move four earth beads in the 10s column upward toward the dividing bar. In the 1s column, move three earth beads upward toward the dividing bar. This gives you the number 93.
Write the number which you want to use in your calculation in the appropriate field. An online abacus may require you to do some of the calculations yourself as is the case in the one described above.