I am afraid you have asked your question in the wrong forum. Please consider reposting this in the Q&A forums, C# category. Please be sure and tag your question with relevant tags, like: C#, WinForms, etc. And make clear in the question exactly what you mean by "add list:" obviously, you want a list to appear, but is this is just a static list the user can't interact with, or is this a list where clicking one, or more, items in the list "means" something ?
~ “This isn't right; this isn't even wrong." Wolfgang Pauli, commenting on a physics paper submitted for a journal