You don't need to add any form inside a .ascx file, in ASP.NET WebForms there can be one and only one form on a page and it already exists in the layout.master file so you don't need to add one and adding one would break things.
If you need to import a namespace keep in mind it it case sensitive.
I recommend study the developer docs and training videos and especially the hello world article should help as far as how to wire up a button and its click event.
Hope that helps,
Joe