Mp3tag
A very-basic crash course in adding covers and metadata to MP3 files
Step 1: Have Mp3tag installed and open on your computer
Step 2: Go to File -> Change Directory
Step 3: Navigate to the file where your MP3s are located and click Select Folder (don't go into the folder - Mp3tag loads the contents of the whole folder for editing, so you need to select the folder itself, not the MP3s inside the folder)
Step 4: Select the file(s) that you want to edit from the list on the right
Step 5: Enter any metadata that you want to apply to those files in the fields on the left (if you're selecting multiple files, don't edit any fields that you don't want applied to ALL the selected files)
Step 6: Add a cover by right-clicking the album icon at the bottom left and selecting Add cover
Step 7: Navigate to the file where your cover image is located, select the image, and click Open
Step 8: Click the save icon in the upper left corner
Rinse and repeat for any and all MP3s you have hiding in the corners of your computer! And if you want to know what any of these other buttons do... don't ask me, because I don't know 😄
