The device you use show already be set up to be a check-in station. Otherwise, you will not see the button which opens the check-in system.
Sign into One Church Software and click on the "Launch Check-in" button in the upper left.
You can also open an individual event and click on the same button in the upper right corner to open check-in for that particular event.
Pro tip: It is recommended to just save the link to the check-in system as a bookmark or desktop shortcut in the browser of the station to help remove the need to sign into the system first and speed start up. See section below for more details.
Instead of clicking on the button above, you can also access the check-in system directly using the following link. Just replace "subdomain" with your account subdomain. This link will show you all the events currently happening. You can then select the one you want to check-in for. If there is only one, then it will be automatically selected.
Each event itself also has a direct link in the following structure. Going there will show all the sessions defined for the event. You can then select the one you want to check-in for. If there is only one, then it will be automatically selected. The event id can be found by navigating to the event within One Church Software and looking at the URL.