using definite an indefinited articles
how to use definite and indefinite articals a, la, el, las, los, un, una, unos
2 Answers
Simply ask yourself which you would use in English. It will work 95% of the time. Of course you will need to know of any odd ones like "unas" which mostly corresponds to "some".
"I just ate some peanuts." - "Acabo de comer unos cacahuetes."