Many dialogs have controls that can stretch to the right when the form resizes. For example, a contact entry might have a series of Labels and TextBoxes for name, address, and so forth. When the form gets wider, it is useful to make the TextBoxes wider to use the available space.
Position the controls. Then set the TextBox's Anchor properties to Top, Left, Right. The rest is automatic.
If you want controls to the right of those that stretch, for example OK and Cancel buttons, set their Anchor properties to Top, Right.