Square keeps its own list of locations. Paddl keeps its own list of sites. Mapping is the step that says which one feeds which, and nothing arrives for a site until it is mapped.
Where it is
On Settings > Integrations, under the Square connection, there is a table headed Square locations. Each row is a Square location with a dropdown of your Paddl sites next to it. Pick a site for each row and press Save mapping.
The rules
One Square location per site. Two rows cannot point at the same Paddl site; the page says so if you try.
Unmapped locations are ignored. Their orders are not read at all, so a location that is not a site you run, such as a head-office test till, can simply stay unmapped.
A location marked Inactive in Square stays in the list so you can see it, but it is not read at all, history included. If a location closed and its site carried on under a new one, map the new location; the old one's takings do not follow.
What you will see after saving
Each mapped row shows Synced to and a date. History for a newly mapped site pulls in the background, so the date moves forward over the next little while until it reaches today. From then on it stays a day or so behind at most, because a day keeps settling for three days after it ends.
Changing a mapping
Pick a different site and save. The history for the newly mapped site pulls in the same way. Takings already recorded against the old site stay where they are, because they were real takings for that site at the time.
When the two lists do not line up
One Square location covers two of your sites. For example, a bar and a restaurant that are separate sites in Paddl but one location in Square. Map it to the site that takes most of the money, and enter the other site's takings by hand. Or merge the two into one Paddl site if they share a team and a rota.
Two Square locations are one site. Two tills in one building set up as two locations. Paddl cannot yet feed one site from two locations. Map the busier one and tell us; it is one of the things we are asked for.
Currency and time zone. Each mapping carries the Square location's own currency and time zone, so orders land on the right day for that site. A site whose takings arrive in more than one currency cannot be forecast as one figure, and the forecast page says so.
Sites you add later do not map themselves. Come back to this page after creating a site under Settings > Locations and pick it from the dropdown.