I want to clear one item in listbox winforms c#

I want to clear one item in a listbox winforms c#.

How can I get the index of the item?

ListBox has a property called SelectedIndex. To remove current selected item you have just to call RemoveAt(int) method.

Example:

int selectedIndex = myListBox.SelectedIndex;
if(selectedIndex >=0)
   myListBox.Items.RemoveAt(selectedIndex);