In the Customiser tab General Options you have serval setting options for the layout of your new MyBoutique WordPress Theme.
Navigate to Appearance => Customize => THEME Option => General Options.
Choose whether you like to display the sidebar of your new theme and gain therefore an extra widget area where you can put more content or leave your theme in the fullwidth layout.
Additionally you can set your sidebar to be sticky and slide along when you scroll your website. Simply tick untick the option you prefer.
Main Navigation Options
Here you have the option to whether you like to nav bar to sticky and follow when you scroll or to leave it fixed on the top. Simply tick or untick the option you prefer.