The ++ operator adds to a variable. The -- operator subtracts . These are shorthand for x = x + 1 and x = x - 1.
int count = 0;
count++; // count is now 1
count++; // count is now 2
count--; // count is now 1
You'll use ++ in almost every for loop you write. The expression i++ at the end of for (int i = 0; i < 10; i++) is what moves the loop forward by on each iteration. Without it, the loop would run forever.