For example say you want to add -5 +2 all that you would have to do is subtract. 5 - 2 = 3. Then you put the negative sign in front. The answer would be -3. Another example would be -2 + 5= 3. Do the same thing 5-2= 3, but now since 2 is less than 5 you would add the negative sign in front. If this still doesn't make sense then try writing out a number line, this helped me because negative and positive numbers are confusing... start with the number line having zero in the middle the counting to the right side go up to 5, so 0, 1, 2 , 3, 4, 5. Now fit the left side with -1 -2, -3, -4, -5. Now use the number line that you created to test these examples. For example 2 do this: start at number -2 then move 5 numbers to the right then you stopped at your answer.
I hope this helped!