See
How to use ArcGIS samples
for help on compiling, setting up the debugger, and running the sample.
If the sample has associated data, you will find that the sample's zip file includes a "data" folder alongside the language folders.
However, you will need to update the sample to point to the location of the data once you have extracted all the files.
Open the solution using Visual Studio.
Build the solution to make the TriangleElement class library.
Use this command in an application with a MapControl and ToolbarControl, or in ArcMap.
Add the TriangleElementTool to the ToolbarControl. The tool (Triangle Element) can be found in the .NET Samples category.
Run the application and add, then choose the Triangle Element tool. Use the tool to add new triangle elements to the map. Use the Select Elements tool to resize and move the triangle elements. Use the Rotation tool to rotate triangles.
Save your map document containing triangle elements or use Save a Copy to save the triangle elements to a pre ArcGIS 9.0 map document file (.mxd).