C# Yield

Unity Engine
1

hi all
if i write ienumerator movement function and in this func write yield return waitforseconds(5f);
it report unknown identifier.
how can correct?
movement func is call in update.
thankful.

2

its yield return new WaitForSeconds() cause the later is a constructor

3

i want when i clicked then my attack animation play complete.
now when i click then attack animation restart .if its play not now complete then again restart if i click.

4

its correct when i use StartCoroutine
thankful.