I'm looking for an idiom that would mean

to talk much and to say very little
to talk about something for 15 minutes what can be said in 1 minute

for example, while at school , You haven't studied at all but you can talk for hours and you make an impression that you know everything
you have to write an essay, you know nothing about the topic but you can write and write for several pages.

Politicians are very good at this, they use several sentences what can be summarized in one sentence.

I'm not sure if I explalained clearly what I mean, I hope so.
I would be grateful if anyone could help me.

thank you
'To go all around the houses' means to talk a lot, but also with the sense that you are avoiding having to give a simple and direct answer.

When she asked him if he loved her, he went all around the houses.

This was a BrE idiom many years ago. I don't live there now, so I don't know if it's still used.

Ther's also 'to beat about (or around)the bush' which is rather similar, perhaps stressing more the avoidance aspect.

Best wishes,
Yes, it's still used Clive, but maybe not so often as formerly