How do you do this? Please, someone help!

a. 6+(-12)+8= ?

b. -23+(-4)+(-12)+(-5)= ?

Adding a negative number just means subtracting a positive number. So, for a, you should replace each +(-x) with a subtraction sign:
6-12+8
Then, you subtract 12 from 6:
-6+8
-6+8=2, so your answer for a is 2.

For b, you first replace the +(-x)'s with -'s:
-23-4-12-5
Then, you just subtract from left to right:
-27-12-5=
-39-5=
-44
So, the answer to b is -44.

a. 6 - 12 + 8 = 2

b. -23 - 4 - 12 - 5 = -44

a) 6+(-12)+8=6+8-12
=14-12
=2
b) -23+(-4)+(-12)+(-5)=-27+(-17)
=-44