How Can I make a Botton in windows control library

Can you be more clear on what you mean, please?

ok. So taking the example of your rich text box, am I assuming correct that you wish to, say, create a button which will add the bold effect to the highlighted text?

If you wish to have your own button, you just need to create a new button class and derive is from System.Windows.Forms.Button. It will have its basic button functions plus you can code any addition functions you like.