Supermarket in MIT App Inventor

I’m trying to make a project that consists of a supermarket that sells food, clothes and appliances, where customers register and buy their products, and ask them to take them home.
But I’m having some difficulties because this is a language I’m still learning, which is the MIT app inventor, so I wanted to ask if anyone could help me or tell me if there is any site that can help me please.
Thank you.