We recommend to use the default settings. If you set mp3Tag to write only ID3v1, you can save much time, but such things as custom genres, pictures, lyrics etc. will be lost.
You can change any field for all selected files simultaneously. To do this, select all the files that you want to edit.
Type the required information into the field(s) that need to be changed. Click "Save" on the right to save changed tags. This may be useful for correcting wrong information for a group of audio files.
mp3Tag can be set to remember what you type into the fields and later to offer previously typed information as a dropdown list (so that you can easily pick out an appropriate value without typing it again). If you want to use the option, activate "Save fields history" in the "Options" menu.
You can simultaneously change as many fields and for as many files as you want.
mp3Tag is capable of doing a way more exciting things. It can extract info from filenames and folder names, download tags from Amazon or FreeDB, import tags from a text file. It can download lyrics and album art for your music. It can rename audio files and sort them into newly created folders.