To remove errors:
1. Understand them: You already know that dividing by zero, "/ by 0", is bad.
2. Find the source of them: The error message points to the source of the error: "at GCDCalculator2.main(GCDCalculator2.java:16)". The number '16' is a line number.
There may be additional steps to understanding and finding, like "Where is division occurring?", "How can that divisor be zero?", etc.
3. Eliminate the source of them/eliminate them: In this case, make sure that the divisor is never zero. Sometimes "protecting" is used in place of "eliminating." If that approach was chosen in this case, I'd rephrase the first sentence to: Make sure that the statement causing the error is not executed IF the divisor is zero.
You can do this on your own, and it's an important, even vital, skill to learn. You need to learn how to debug and fix a simple program like this one so that you can then scale those skills as the complexity of your programs increases. Having someone tell you how to fix errors is not the same as learning how to fix them.
Get to work.