The page would typically be written as ASP (Windows server only) or PHP (Linux or Windows servers) code to interact with the database via an ODBC connection.
The back end is more often MySQL or Microsoft SQL Server than Access but any ODBC database can be used.
Basically the saving sequence is whatever the web server feeds to the database engine in order of arrival but it depends on how the connection is managed. Concurrent edits on the same records need to be intelligently managed.
It is quite a learning curve from an ordinary Access database.
The other option is to use the web features built into Access 2013 but I have never used this so I can't tell you anything about it.
