We've put together six potential reasons why your Mac is running slowly, and troubleshooting tips to help speed it back up.
Solution: Go to your App Store to check for updates on your Mac and approve those (or if you're not in a huge rush, be sure to install the update the next time your computer alerts you.)
You can also check for system updates by going to the Apple icon in the top left corner and select "About this Mac" and then clicking "Check for updates."
Solution: Check your hard drive space by clicking the the Apple icon in the top-left corner and then selecting "About this Mac."
Next, toggle over to the "Storage" section and wait for it to calculate how much space you're using.
This will open a new window with many tools for clearing out space on your hard drive, as well as readings on how much space every application, document, and more is taking up.