.NET Stored procedures or functions are developed using Microsoft Visual Studio and deployed using the tightly integrated .NET Deployment Wizard which is a feature included in the Oracle Developer Tools for Visual Studio. You can develop and deploy your .NET stored procedures from Microsoft Visual Studio.

After deploying, a .NET stored procedure can be called from within .NET application code, from SQL or PL/SQL, from another .NET, PL/SQL or Java stored procedure, from a trigger, or from anywhere else a stored procedure or function call is allowed.

This product is included with the Oracle Database on Windows installation. Further upgrades are installed as part of the Oracle Database Access Components (ODAC) releases, however Oracle Database Extensions for .NET must first be installed and configured before it can be upgraded.

Downloads: 

Oracle Database Extensions for .NET is included with Oracle Database for Windows. For Oracle Database 12.2 and earlier, upgraded versions are available via ODAC. Before upgrading to a new version, please read chapter 2 of the Oracle Database Extensions for .NET Developer's Guide for more information. 

Download ODAC

Guided Walkthough: 

 Oracle By Example: Developing and Deploying a .NET Stored Function