Wrap your code to do this in Component (the IComponent interface or the Component object). Once you have created your component and exposed its properties, methods, and events publicly, then you can use it in your solution. To do this;

1. Copy you assembly(s) into the Pega Robotics (OpenSpan) installation folder along with any supporting assemblies required. This directory is generally C:\Program Files (x86)\OpenSpan\OpenSpan Studio for Microsoft Visual Studio 2015 for Pega Robotics Studio. The plugin will be slightly different.
2. Add the component to your Toolbox by right-clicking on an empty area of the Toolbox and selecting "Choose Items".
3. You can then locate your component and add it to the Toolbox.
4. From there, you may drag it onto an automation like any of the other objects on the Toolbox.