From my understanding flipping the switch is making changes to some (not sure which) initialisation parameters.
Secret SauceWhat is the big deal with Oracle In-Memmory Database? Well, it is fast - really, really fast. DRAM is faster than Flash, and Flash is faster than disks.
Another big deal is the dual format in which the data is stored. The data is stored in a columnar and row fashion, both in memory. This means that analytical type queries can be answered by the columnar storage while other type of queries can be resolved using the row storage. And yes, the optimizer is aware of columnar storage as well.
Oracle takes care of storing the data in both formats, this is done completely transparent. It is simultaneously active and transactionally consistent. The secret sauce is the dual format storage, this is what it really makes it fast.
The columnar format of the data is memory only, the row format is stored in memory and persisted on disk, just as it is nowadays. In order to take full advantage of this you don't need to learn anything else - from a developer point of view.
During DML the affected data is marked as stale (in memory) thereby limiting the overhead. You can pick and choose which tables, partitions, columns you want to have in columnar format.