treeView1 error

Hi everyone,
the error "The name 'treeView1' does not exist in the current context" is showing up, how do i fix this??
(I'm using .NET 4.5 vs 2010)

note: i do not know much about c#, the course is about GUI and we have to use c#

hope for answers and thanks in advance.

Open up the form editor and drag a treeview control onto the form.