Lesson 66 tells you about the position of adverbs generally. This lesson shows how to use ago, already, late, lately, later, just, still, then and yet to talk about when.
I'll be here again on Friday.
I'll see you then.
First, I got up. Then I had breakfast.
(the second thing I did)
It's six o'clock now. The shop closed half an hour ago.
(it closed at half past five)
Use ago with past simple formation (Lesson 21) only. For other formations, use before:
It was six o'clock. The shop had closed half an hour before.
The boss arrived twenty minutes late.
(after the correct time)
We arrived at nine. The boss arrived twenty minutes later.
(at 9:20, but there was no correct time to arrive)
I'll see you later.
(at a time in the future)
I've been ill lately.
(my illness started a short time ago)
I've just seen a film about lions.
(a very short time ago)
He's just going to leave.
(very, very soon)
They had already eaten when I arrived at nine.
(they ate before nine; by nine they had finished)
Is he still asleep?
(I know he was asleep; what about now?)
Is he asleep yet?
(I know he was not asleep; what about now?)
She hasn't finished it yet. (= She is still doing it.)