How location ends up in a photo
When a phone's camera app has permission to use location, it writes a GPS block into every photo. That block holds latitude and longitude, and often altitude, the direction the camera faced and a satellite timestamp. Outdoors the coordinates can be precise enough to pick out a single building, which is why a photo taken at home and posted publicly can reveal an address.
As soon as you upload a photo, the tool reads the file and shows any coordinates it finds in decimal degrees, so you know whether there is anything to remove.
What the GPS metadata remover deletes
The entire GPS block is removed, not just the latitude and longitude, so altitude, direction and GPS time go with it. XMP metadata is dropped as well, because it can hold a second copy of the location, and the small embedded preview thumbnail is always removed.
Only GPS location is ticked by default, and Remove all metadata is off. Camera & lens, date taken and software stay in the file unless you tick them too, which is useful when you want to keep a record of when and with what a photo was taken. The orientation tag is kept, so the image still displays upright without its pixels being rotated. Tick Remove all metadata if you would rather clear everything, in which case the photo is turned upright before the tags are deleted.
Stopping location tagging at the source
To stop new photos from carrying a location, turn off location access for the camera. On iPhone this is under Settings, Privacy & Security, Location Services, Camera. On Android, look for a location or geotag option in the camera app's settings. Some share sheets also let you exclude location when sending a single photo. For pictures you have already taken, this tool removes it after the fact.