Compound assignment operators combine an arithmetic operation with assignment into one step. Instead of writing x = x + 5, you write x += 5. The result is identical, but the code is shorter.
int score = 100;
score += 10; // score is now 110
score -= 25; // score is now 85
score *= 2; // score is now 170
score /= 5; // score is now 34
Java also supports %= for modulo assignment. Writing x %= 3 is the same as x = x % 3. You'll see compound assignment everywhere in loops and accumulators, so get comfortable reading it.