Read Windows installation guide for Oracle
very important, set up Microsoft Loopback adapter with STATIC IP
and when installing ORacle have that as the ONLY enabled network device.
That way, Oracle will run on the same static IP no matter what your workstation
gets for IP to get on web, LAN, etc.
You got quite a bit of a learning curve just to get database running.
Then start learning ODP.NET to communicate C# to Oracle from application.
The Oracle DB download on OTN permits free use for the purposes of developing, testing, prototyping and demonstrating your application, just not production use.
Chapter 2 of this book discusses how to install Oracle, though you could figure out the install without it since most of the default selections are made for standard IT environments.