Hi @fireblaze987 welcome to MusicBrainz!
I hope you will enjoy your time here, listing your CD's and digital albums!
About adding Cover Art, @InvisibleMan78 gave you a very good tutorial but I like to add a bit to the tutorial: when you scan cover art, best do it at more than 300 dpi, so you can make a nice sharp image that won't be too small. For making cover art out of your scan, make a new blank image at 72 dpi with height 1600 px and with width depending, sometimes 1600 px sometimes 1700 px, you will see when pasting the scan into the new image, what the shape should be. Why choose 1600 px at 72 dpi you might ask? It is an accepted standard for the web, that artists have to follow when sending in their cover art to distributors of the release like GooglePlay and Amazon. If you have any questions (maybe you are not familiar with a graphics program?) about creating the right Cover Art for the Cover Art Archive, do ask me and I will be happy to help you!
More in general, if you have any questions, do ask here in the Forum! Because there are always kind and very helpful members with a lot of expertise here, to be there for you