I am Romanian so I can explain :))) The definite article is put at the end of words (for example "femeia" instead of "femeie") and it is the equivalent of "the". The indefinite article ("un, o" or "niște") is used when refering to things (such as "un măr" = an apple, "o femeie"= a woman), but it is NOT used when we say something or someone is something; so, "Eu am un măr" is "I have an apple", but "Eu sunt femeie" means "I am a woman" - notice how the indef. article "o" is missing, because we use case 2. I don't really know how to explain so I hope you get the idea, but i'm always happy to help. Good luck in your adventure learning Romanian!!