1) Select the edit->Undo or undoing action command to reverse the last action. Some actions can not be undone.When this is the case the Undo icon is grayed out.

Select the Edit ->Redo command to recover the last action undone.

Select Edit -> Cut command to cut objects.

Select Edit -> Copy command to copy objects.

Select Edit->Paste comand to paste object at the desired locations.
Edit -> delete command or Delete command in the contextual menu.
Select the object or object you wish to delete ,either in the specifiaction tree or in the geometry tree.