Click on Register item in the program menu. A key input form will appear. The registration key is too long, so better use a clipboard to copy (Ctrl+C) and paste (Ctrl+V) the key.
2.
If the registration email has a regkey.txt file attached, copy this file to the folder where the MP3 Tag Editor software is installed.
3.
If you have a disc, press Register button on a program page in the CD Shell.