The easiest way to make a Moodle site with logo on the front page:
- Go to Admin -> Configuration -> Themes
- Choose "standardlogo" and then save changes (some instructions will be shown).
- Upload a file called logo.jpg into your Site Files.
You can also upload logo.jpg into the main Moodle directory (via FTP, say). If you do neither of these, then the Moodle logo is shown by default.