Hams trade grid squares (Maidenhead locators) instead of addresses. Turn a latitude and longitude into a 6-character locator, turn a locator back into a spot on the map, and work out distance and beam heading between two stations.
North and east are positive. West longitudes are negative (Lethbridge is about −112.84).
Your location is worked out on your device. Nothing is sent anywhere.
Enter two locators, or lat,lon pairs like 51.05,-114.07.
The world is cut into 18 × 18 fields (two letters, AA to RR), each 20° of longitude by 10° of latitude. Each field is cut into 10 × 10 squares (two digits), 2° by 1°. Each square is cut into 24 × 24 subsquares (two letters, a to x), about 9 km by 4.6 km around here.
A 4-character square like DN39 covers a big area, roughly 140 km by 110 km in southern Alberta. That's why it's a friendly way to share where you are without giving out an address.
Distances use the great-circle method on a round Earth (radius 6,371 km), measured between square centres. Short path is the direct heading; long path is the way around the other side of the world.