First Go to Settings > Reading from your WordPress Dashboard and make sure that your “Front Page Displays” option is set to “Your Latest Posts”. Even if you don’t have to display latest posts on your frontpage you will still have to make sure that the frontpage is set to that option. Don’t worry, you can easily replace the Posts with widgets by adding widgets from Customize > Frontpage > Frontpage Widgets. Once you add the widgets, the posts will be automatically replaced.
Customizing The Slider
Then Go to Customize > Frontpage > Slider to setup the slider:
Adding Widgets to your Frontpage
Optimizer frontpage can be built with beautiful widgets. To add widgets to your frontpage, Go to Customize > Frontpage > Frontpage Widgets and click the “Add Widgets” button to add widgets.