Self Checkout

asking for a friend..lol
but seriously out of curiosity, how do shoplifting laws work in a situation where someone isn't scanning items (not switching barcodes), say items like food or household items and an employee catches them? if I haven't paid or left the store, is that considered shoplifting?
what about if I stick something in my pocket and approached in store, is that shoplifting if I'm still in store?