when i save my tracks in a new folder, it indicates that it is a file rather than an MP3 file, is there a difference between the MP3 and .mp3
If you use “Save” in the Audacity File menu it will save an Audacity Project. This is not an MP3 and is not any sort of audio file.
More information about the Audacity Project format here: http://manual.audacityteam.org/o/man/audacity_projects.html
And should you want an actual MP3 sound file, use File > Export. That also presupposes you installed the “lame” software. Audacity will not Export MP3 by itself.
And don’t add dots in the file name of the exported MP3 unless you add “.mp3” (without quotes) to the end of the name. See here http://manual.audacityteam.org/o/man/faq_opening_and_saving_files.html#extensions .