If you add positive 5 and positive 5, you'll get positive 10.
If you add positive 5 and negative 5, you'll get positive 0.
If you add negative 5 and negative 5, you'll get negative 10.
-5 + 5 = -5 + 5
5 + 5 = 5 + 5
- 5 + -5 = -5 + -5
Does that help your question?