At first, you have to open the MP3 or other audio or video file. To do that press on the "Open" button on the toolbar or select "Open" from the "File" menu.
You can also drag and drop the audio or video file to open it.
Step 2 - Edit Metadata and Album Art
Afterward, select "Edit Metadata" from the "File" menu.
Then by pressing the "Add" button of the toolbar you can add metadata keys and values.
You can select as a metadata key one of the predefined values or add your own.
To set album art check on the "Album Art" checkbox and select either "Same as Input File" to keep the original album art or press on the "Browse" button to select your own image.
Step 3 - Specify Output Format Settings
Press on the "Output Format" button to specify various output format settings or leave the default ones.
Step 4 - Get the Result
Lastly, select "Save Whole Clip" from the "Cut" menu to get the result file.
In case, you want only a part of the MP3 file, after selecting it, you can choose also "Cut Only Selection" from the "Cut" menu.