For a Visit Request for a location that doesn't require authorization, an option is provided in the form to check-in immediately. This will mark the visitor(s) as having arrived automatically.
For the Ad-hoc Visit form, all visitors will be checked in automatically.
If a request is put in ahead of time, then when the visitor arrives you should go to the request and there you will see the visitors listed underneath the request (this is because a single request could have multiple visitors, if a group is visiting from a company). There you will see the option to "Arrive" on the visitor record under the request.
Alternatively, click the Scan Visitor ID to scan or enter in their ID card number. The system will then lookup a particular visitor and take you to that visitor screen. You can then click "Arrive" to mark them as having arrived.
Once a visitor has arrived, the request will show as Green:
Next Topic: Checking Out Visitors