Take a moment to figure out if your mouse or trackpad scrolls in the traditional direction, or the "natural" direction.
Traditional scrolling means that when you drag down, the top of the page goes up off the screen. "Natural" scrolling, as Apple calls it, means that dragging down brings the top of the page down onto the screen.
Wait, Are You Scrolling The Right Way?
"Natural" scrolling is bullshit, and anyone who does it that way is wrong.
There's nothing natural about "natural" scrolling. Just pop into System Preferences real quick and fix it, and we'll pretend this never happened.