How to add Save file Dialog Box using C#

Question

I need to implement something similar to Notepads' save option. Assuming I have a button placed next to a RichTextBox, what I want is, when this button is clicked, a Dialogue box will open up, which will look similar to the one that appears when Save As is clicked. I would like to save the content of the RichTextBox in text format, by entering the name of file in the Save Dialogue box.