To upload the main logo for your site, go to Design › Edit Theme › Header › Logo. Here you will be able to use the file upload field titled Logo. For best results, we recommend a file with a height of 80px and the natural width of the logo that scales with that height. The image should also be a transparent .png file.
The favicon is the small icon that is most often seen in the tabs for most internet browsers. You can upload your favicon by using the file upload field title Favicon. It should be a square file with the following properties: