The title, artist information, composer, track number and album art is stored within the mp3 as a set of tags. They can't be changed by simply changing the name of the file. The tags can be edited by popular mp3 player software such as Windows media player or iTunes. However they do not provide the advance functionality required to modify groupes of mp3 files. For instance, if the mp3 files that you have do not have any of the mp3 tags set, but the files are named according to the title of the song, the popular media player won't be able to set the tags to the filenames.
Mp3tag is a very neat tool that provides a lot of functionality to edit mp3 tags. It excells at batch processing (processing a group of files). It is very simple to grab the song title from its filename or even grab parts of the filename and set different tags.
Mp3Tag can be found here. The software is free and it does not have any malware. Its windows only, and it can be downloaded from here. Its got a few help pages that are very useful when you are starting up.
Adding album art
With Mp3Tag, adding album art to an mp3 file is easy as drag and drop. All you have to do is find the album art from Sri Lanka CD Album Art. Click on the album thumbnail to open up a bigger version. Then simply drag the image and place it album art section of Mp3tag and hit save.
If you want to add the art for a collection of tracks, or for all the songs in one album, then simply select all of them and drag and drop the album image to mp3Tag's bottom left corner where the album art is displayed. Hitting the save button will save the change.