Back up all the documents, files, pictures, videos, and other accumulated stuff on your Mac. You can do this with the built-in Time Machine tool or copy your folders manually. Place the SSD in the case, then connect it to your Mac using the included USB cable. Open "Disk Utility" and format your SSD to A PDF format if available, or to "Mac OS Extended with GUID partition scheme" (on older versions of macOS). For additional data backup, use https://www.salvagedata.com/. I renewed my old 2014 iMac this way, and the effect of the SSD exceeded all expectations.