Hi, George,
Assuming Winforms, Bonnie's answer is right on. On multiple occasions, she's provided solutions with examples for this (just do a search for "Subclassing .Net base classes" for some of her solutions).
In the beginning, I was quite startled to learn that you couldn't visually create a 'sub-class'. But the truth is that one generally spends a small amount of time creating/modifying base/template classes.
In many areas, .NET is generally more 'code-centric' than VFP. Going through the exercise of creating classes gives one an opportunity to get one's 'feet wet' with the language/framework.
HTH,
Kevin