Q: Oracle Exadata datafile distribution I'm new to Oracle and curious of how Oracle Exadata handles database files. Do we have to assign the disk to a database file as we do with Microsoft or is this handled by Exadata? 

A: I do not know what you mean by the "Microsoft" way, but Exadata uses ASM.
Administering Oracle ASM Disk Groups on Oracle Exadata Storage Servers
http://www.oracle.com/technetwork/database/availability/maa-exadata-upgrade-asm-2339100.pdf
ASM is not specific to Exadata or any hardware, you can use it on any supported platform, even on Windows, so you handle database files just as in any other environment with ASM.

A: The storage interaction on Exadata is done via ASM on the database servers, that talks to the cell storage servers using an interface layer called libcell rather than the usual disk IO layer. The InfiniBand network is used for all storage interactions.
Apart from the initial setup (which is done as part of the Exadata deployement), the databases are handled exactly like you would handle a database on ASM on general-purpose hardware. It is transparent for day-to-day tasks like creating/extending/dropping datafiles or tablespaces, also transparent for backups (as long as you use RMAN).
There are a few recommendations for storage parameters that are specific to Exadata (regarding extent sizes, cache parameters), you get access to HCC compression, and you can do IO resource managements at the storage level. (Plus all the cell offloading goodies.)  But apart from that, for every-day care and maintenance, they look just like any other ASM-based databases.
This is the same for bare-metal database servers and for virtualized database servers (since X5). The virtual machines get virtualized InfiniBand connections, and ASM uses those the same way it does on bare metal.
If you want to know more details about how the cell servers themselves are configured, I encourage you to go have a look at the docs, they are pretty comprehensive. A nice starting point to get a feel of it would be the cell admin guide, the Administering Oracle ASM Disk Groups on Oracle Exadata Storage Servers has a simple diagram for how the pieces interact. There's also a section on the Oracle support site that is dedicated to Exadata topics.
