That depends on the class.
If the class requires a constructor, you need to use the constructor node and select one of the constructors from the list. This will give you a reference you can use.
Some classes are static and don't require calling a constructor. You can use those by dropping a property node, right clicking and selecting Select Class>>.NET>>Browse...
If you have no experience working with .NET, you should look for some examples and tutorials on this site.
___________________
Try to take over the world!
