After you’ve created the menu, you’ll probably want to set up the Homepage. Seattle is a multi-purpose theme and at this moment it has 12 homepage layouts. To set up any of these layouts as your homepage, you need to navigate to Pages > Add New. After you create a new page, just set its title and choose the page template you want to use.
After you create the Homepage, navigate to Settings > Reading and adjust your frontpage settings as shown on the screenshot below:
After you do this, navigate to Theme Options and upload your own loader, logo, homepage background image, video, etc.