Favicon - Favorite Icon is also known as a Shortcut, Website, Tab or Bookmark icon.
Favicon helps in making your website look more complete and classy, it shows in the left side of the page or open tab. Including the favicon really shows the views that you've took the time to add every detail to the website.
The basic gig includes 3 sizes ( 16x16 , 32x32, 64x64 ).
For Different OS(s) like android, iOS, Blackberry and symbian, size will be different you have add a gig extra which includes complete package for all of them. What I need from you is, editable (source) file of your logo.