Using the virtual soroban:
There are 2 ways to enter a number in the virtual soroban:

Using the keyboard, enter the number in the field above. Press the "Update" button when done. The soroban will update to display the number you entered.

Move the beads by pointing with your mouse and clicking the left button. The number will update automatically.

To set the soroban to 0 use the "Reset" button.
More information: How to enter a number in the Japanese abacus

A short history of the abacus:

The Abacus represents the evolution of our hands as tool used for counting. The early abaci, or rather, the early counting devices were lined boards on top of which the user would place pebbles. Each pebble on the board represented a different quantity depending on over what line of the board it was placed.

The Romans improved the concept of the counting board by making grooves on the board so that the pebbles wouldn't fall out of place.

The Abacus with wires or poles running through the center of the beads was invented in China.

The Japanese, adopted the Chinese Abacus and later they modified it by removing one bead from the top row and one bead from the bottom row. The Japanese version of the Abacus is called Soroban.