Your goal is to isolate the variable (x)
2x+8=16
Use the opposite sign to eliminate 8 from the left side (1st step to isolate x)
What you do to one side you must do to the other so:
2x+8-8=16-8
Simplify
2x = 8
Now use the opposite sign of 2x to isolate x (in this case division is the opposite of multiplication, 2x represents 2•x so 2x/2 will cancel it out)
2x/2 = 8/2
Simplify
x = 4