-2 times -3 is 6. The negative signs cancel each other out, and you are left with two times three, which is six. If you were doing a question like -2 times -5 times -3, the negative signs wouldn't cancel each other out, and you would get -30. The key do knowing whether you need a negative sign in your answer is this: if you have an even number of negative signs (0 included), your answer will be positive, and if you have an odd number of negative signs, your answer will be negative. When doing multiplication problems like these, 1. Find out if your answer will be negative or positive, 2. Multiply like normal, and 3. Write your answer down (don't forget the negative sign, if it is needed!)
Hope that helps you!