Step by step
Switch business
Click the business name at the top left and pick another one. Nothing is mixed: products, stock and money stay in their own business.
Add a business
On the Businesses page, press "New business". It gets its own free trial.
Archive a business you closed
Settings › Business profile › Archive business. It disappears from the list and nobody can work in it, but its data stays. Restore it any time from the Businesses page.