Set certain font/color in RichTextBox

Question

I've drop a RichTextBox onto a form to enable the users to type in the data in the RichTextBox.. but now i want the system enable the users to customize the font, size etc for some of the selected text, how am i goin to do so ?? P/S : I want the system enable the users to customize their selected text to any types of font they prefered(I mean the font could be any types base on the customer preference) .. Anyone help pls .. Thx in advance