ODBC is a method by which applications can connect to multiple different Relational Databases by using a standard interface. For example, Oracle, SQL Server, DB2, Sybase, etc all have slight differences in their SQL language and features they offer. ODBC distills the differences and creates a common language. That allows me to link my Access FE to a SQL Server BE and create queries and forms, etc. But, tommorrow if I want the BE to be Oracle, I can simply relink the tables to point to the Oracle database. Each publisher of an RDBMS creates his own ODBC driver so to link to Oracle, I need the Oracle ODBC driver, to link to DB2, I need the DB2 driver. But my Access application can swap BE's and not require any change except the relink.
ODBC data soruces used by Access are typically on a server on your own in house LAN. And each PC should have a wired connection for safety. WiFi connections are unstable and can corrupt your database. While it is possible to link to databases using an internet connection, it is dreadfully slow and generally not usable which is why Access is not usually used to create applications that will be used by remote users. There are ways around this though. Citrix and Remote Desktop are both excellent products that allow you to distribute your Access application to users around the world and have them all linked to the same BE data base.
Access CANNOT be used from a typical cloud location such as oneDrive. The data protocols are different and they do not allow sharing of the application by multiple users. Cirtix and Remote Desktop are your best bets. Azure is a possibility but that can also be very slow if not configured correctly.
