x is some number. Think of it as a placeholder for a value. You can think of it as a box if the letter confuses you.
We are adding another placeholder to x, in this case b. To get x all by itself, we have to do something to both sides to get the 'b' to move over. We need to undo the addition. So we subtract b from both sides
x+b > c
x+b-b > c-b ... subtract b from both sides
x > c-b ... notice how b-b turns into 0 and goes away (since x+0 = x)
Final Answer: x > c-b
This means "x is greater than the quantity c-b" or "x is larger than the quantity c-b"