840 gps maps
The manual is often obscure or silent on many things but in this case clear
https://www8.garmin.com/manuals/webhelp/GUID-16B12CFE-F96E-4DE9-9F5F-8C4A5936D3B9/EN-US/GUID-8CDC63DE-5050-41AB-A023-BAE0E621DB42…
Did you consult the manual?
https://www8.garmin.com/manuals/webhelp/GUID-16B12CFE-F96E-4DE9-9F5F-8C4A5936D3B9/EN-US/GUID-8CDC63DE-5050-41AB-A023-BAE0E621DB42.html
It is worth a being familiar with the basic features to ensure you get best value from your device