Welcome to e107! Sorry for the delay in answering your question.
The frontpage content is defined by your 'Frontpage' setting in the Admin Area (Admin Area > Settings > Frontpage). Here you can select which content should show on your frontpage. By default, for the bootstrap3 theme, this is the 'Welcome message'. For the voux theme it may be different.
Depending on your frontpage setting, you can show news, a custom page, etc.
The bootstrap3 layouts, have menu areas. The menu areas you see at the bottom of the frontpage after installation are there by default, but you can change them in the Admin Area > Menu Manager.