After creating the custom theme in themes directory then you need to activate this theme. So first of all you need to go in WordPress Admin and then click on the Appearance menu and inside this you will see the Themes menu. Then you need to click on Themes menu and the you will look your custom theme here and then click on activate button. Finally you have activate your theme. Now your project will be run on your custom theme.
Appearance Menu -> Themes -> and then click on activate button of particular theme.