Can I make a suggestion?
The next time you login to your Moodle site as an Administrator, take the time to look for and read any Moodle doc link on the page you happen to be in. You should find the link in the footer. For instance Theme settings tells you all about what settings are available.
In most, but not all, Moodle 2.x.x themes have custom settings pages, which you will find in the links listed under Settings > Site Administration > Appearance > Themes > ... Listed at this point you will see a list of Theme names, including Formal White. If you CLICK this link you will find the Custom Settings page associated with this theme. It is in this settings page that you can add your logo. All the instructions how to do this are in that page.
I hope this helps in the Moodle maze or theme development.