"Dette er den tolvte ølen min."
Translation:This is my twelfth beer.
wow, it was only a minute ago you were only on your seventh beer. Slow down!
Kan du sier "Dette er min tolvte øl" eller bare "dette er tolvte ølen min"? Hvorfor trenger jeg å bruker "den" her?
"Dette er min tolvte øl." is fine. Or "Dette er DEN tolvte ølen min." I must admit, I have never needed this sentence.
You need to use den/det when you have an adjective (same for the green house: det grønt huset; the twelfth beer: den tolvte ølen).
I'm not a hundred percent sure you can say the first thing, but it doesn't sound very strange.
Also, just a little correction: it should be 'å bruke' instead of 'å bruker' in the last sentence.
This is definitely one of the essential sentences you need know how to say if you are going to Norway. ;)
Realistically though, unless you're a millionaire you're only going to say that when you go down to Denmark for the cheap booze because in Norway, beer (just like everything else) is really frickin expensive, also at most parties you're expected to bring your own drinks because the host would go bankrupt if he had to buy multiple beers for the guests.