The four mathematical operations, addition, subtraction, multiplication, and division can all be performed using the abacus. By moving the beads according to the values being added or subtracted and using complimentary numbers to account for too many or too few beads, one can calculate large arithmetic problems. Below is a link to an instructional video that explains how to do addition on the Japanese Soroban.
Click here for VIDEO "The Japanese Soroban Abacus, Part 2: Addition" 

The Abacus Today

Click here for VIDEO "SMART Academy - Soroban Mental Arithmetic Training Academy"