>Hi everybody,
>
>I'd like to be able to provide a file extension (s ?) and in my code only save files with these extensions.
>
>I'm a bit confused as to what to use for these extensions textbox.
>
>Any suggestion?
>
>Thanks in advance.

Are you using the SaveFileDialog class?
If so use the Filter property. Something like this

sfd.Filter = "Image Files(*.BMP;*.JPG;*.GIF)|*.BMP;*.JPG;*.GIF|All files (*.*)|*.*";