Smart Lighting
In the new Samsung SmartThings mobile app, you can find Smart Lighting by clicking the button at the top of the main screen, select SmartApp, then select Smart Lighting.
Fair warning that the SmartApps screen in the new SmartThings mobile app has been really quirky for people lately. Sometimes not showing SmartApps at all or not letting you tap on a SmartApp.
Virtual Switches
Unfortunately, SmartThings has not exposed an interface for creating virtual switches in the new mobile app yet. You can create them manually in the SmartThings IDE though.