Does using a scroll wheel on your Mac feel...wrong? You're not alone.
Back in 2011, Apple introduced what they call "natural scrolling." The idea was to make using a trackpad feel more like using a touch screen, like on the iPad or iPhone. On those devices, scrolling up means "dragging" the screen down, and vice versa. When you're using a touch screen, this feels intuitive, and Apple wanted the experience to be consistent in macOS.
When you're using a scroll wheel on a conventional mouse, however, so-called "natural" scrolling feels anything but. You're not dragging anything; you're turning a wheel.
You can toggle natural scrolling in your Mac's system preferences, but there's no default way to make the touchpad behave one way and scroll wheels another. Happily, a third party program called Scroll Reverser lets you use different settings for your trackpad, mouse, and even Wacom tablets.
To get started, download Scroll Reverser. The application comes in a ZIP file, which you can unarchive on your Mac simply by opening it.
Next, drag Scroll Reverser to your Applications folder, then start it up. You will find a new icon in your menu bar.
Click the icon, then click "Preferences" to configure your scrolling settings.
Make sure "Reverse Scrolling" is enabled, then check what you'd like to reverse. Any device checked here will do the opposite of the system-wide setting. So if you have natural scrolling enabled in system settings, any device checked here will do the opposite.
My recommendation: leave natural scrolling on for your trackpad and tablet, but reverse it for your mouse. But ultimately it's up to you.
While you've got the application open, head to the "App" tab.
Here you can disable the menu bar icon, which can free up some clutter. You also have the option of automatically starting Scroll Reverser when your Mac starts up, which is a good idea if you find the application useful.
And that's all you need to know! With a little configuration you can use your trackpad with natural scrolling and your mouse without it, an option that should have been available all along.