The sidebar
Sell, Buy & stock, People, Money, and Setup are groups. A cashier sees fewer items than the owner. If a screen is missing, the role does not include it. See Users and roles.
Search
The search box in the header finds pages. On a phone, use the magnifying glass.
Sync icon
The cloud icon is the queue. A number means this device still has sales or edits that have not reached the server. When the internet returns they send themselves. Do not close the day while that number is sitting there. See Day close.
Offline banner
A bar at the top means this device has no internet. You can still sell. You cannot open the register, close the day, check a promo code, or issue a purchase return. The full list is What needs internet.
Full screen
The expand control hides the browser chrome on a counter tablet.
Next: Company name, logo, and NTN.