Imagine the standard openGL window

**[-1, -1 .. 1, 1]**. Placing objects in here is not very intuitive if you want the origin (0, 0) to be at the bottom left corner. So you subtract (1, 1) from everything you draw, moving the origin (0, 0) to the bottom left corner (-1, -1) and resulting in a now visible window

**[0, 0 .. 2, 2]**. This offset is static, but you can of course add other offsets to further move the window. For example, if the player moves right, you add an additional (1, 0) so the window will be

**[1, 0 .. 3, 2]** or if he jumps, you could add (0, 2) so the window will be

**[0, 2 .. 2, 4]** (both times, the origin is no longer in the window). A consequence of this (and also your goal) is drawing only a certain number of objects, namely those that lie in the window. In a side scroller, you will rarely move to the left, so everything with an x-coordinate smaller than 0 (taking the offset into account) won't ever be drawn. If you want it to be drawn, just reverse the x-direction of the offset. If it's still unclear, I could prepare some graphics for you