Sir this is my first post in c# section:

I want to apply this format to textbox

123,456,789

What type of textbox should I use?
Textbox or MaskedTextbox

and how to apply format like this 999,999,999

Is there any specific property in propery window or I should use some procedure?

Please help

I think the first step would be to format your number to the string you want to use in that textbox.

https://www.google.com/search?q=c%23+format+number+to+string seems to find plenty of priors so let's skip to the textbox.

You didn't ask about a popup so in C# the textbox has properties and it's as simple as

tbSettingText.Text = "Initial text contents of the TextBox.";

So now that you have your formatted string, you seem to be ready.