I have just downloaded the trial incase I cant work with this app. I want to add my own image or artwork to an audio recording I have made but cant work out how to do it?
Highlight the song (or multiple songs) that you want to add artwork to. On the tag panel there is an artwork preview that will show a blank image. Right-click on that and choose Add cover. In the browser window that pops up find the art file you want to apply, and you are good. Make sure you save the changes.
A couple other tidbits. If you don't want to do a secondary click and select "Add" from the menu, you can drag and drop the image file into the Cover Window in the Tag Panel, or you can copy an image and then paste it in the Cover Window (either by menu or keyboard shortcuts like any other copy and paste in macOS). You can also highlight existing cover and use Delete to remove just that cover from the selected files (you can have multiple covers on each file, if you so choose).
I would also recommend checking out this post and the other documentation for Mp3tag as there are a lot of powerful capabilities and shortcuts if you spend some time to learn how to use them little by little. Basics and Overview