How to add tag information in MP3 files

Adding tag information in mp3 files is a good idea to make the mp3 file carry its title, cover art, artist name, track number etc within it. You might have seen that these tag information appear while playing any mp3 file in the music player. In apple ipod, you may hear these tag details also. There are so many softwares which can add tag information in any mp3 file but most of them are paid.