What is a difference between "at the point and on the point of?

What is a difference between "at the point and on the point of?
Please help me!

You’ll have to include a specific sentence that bothers you, Xx. Both forms can mean the same thing, and they also collocate differently:

I am at the point of no return.
I am on the point of returning this lemon.

I have a sentence:
I was (at the point / on the point of) going out when the telephone rang.

I don’t know what these phrases mean and that is why I can’t choose what suits the best to this sentence.
If you explain me what is going on i will appreciate:)

to be at a point - be at a certain place or time
to be on the point of - to be about to do something

I need help, again.;p
Could you explain me what are the differences between:

How long have you learn English?
How long have you been learning English?

He has slept for ten hours.
He has been sleeping for ten hours.

It has snowed for a long time.
It has been snowing for a long time.

How long have you learn English?-- No good.
How long have you been learning English?-- OK

He has slept for ten hours.– He may be awake now
He has been sleeping for ten hours.-- He is still sleeping now

It has snowed for a long time.-- It may be finished now
It has been snowing for a long time.-- It is still snowing now.

Could you please explain the differences between…?

The phrase ‘explain me’ does not exist.[YSaerTTEW443543]

TOEIC listening, photographs: Stacking boxes[YSaerTTEW443543]

I would like to say:
“How I prepared to go to a party.”
Is it correct? Or should I change preposition?

It sounds OK, Xx.

May I say: “I was ready to gain the mountains”?

What do you mean by that?

I’d like to say :“to achieve the summit” but I don’t know how it says

Well, I suppose that you could ‘gain the summit’, but you cannot ‘gain the mountain’.