Audi 1.8 turbo petrol. I bought this back in april and the guy said it drinks a bit of oil.
You don't say how old your car is.
Sorry to sound patronising, but if the seller said it drinks a bit of oil, why did you buy it? I would have been put off straight away. Surely there must have been other Audi A3/4 or even 6's with this engine for sale at the time?
There has been a more recent issue with the 2.0T engine using excessive oil, and Audi have replaced the pistons under goodwill, even if the car is out of warranty, but unfortunately this won't be applicable to your car (I presume your car is 'older' anyway).
Some Audi's display an orange oil warning light which advises to top up as soon as possible, but if the oil light displayed is red, then the engine should be switched off immediately.
The handbook should explain the relevant action with your particular oil light.