"I work at the newspaper."
Translation:Eu lucrez la ziar.
It's simple. The definite article (whether singular or plural) is dropped if: (1) the noun is preceded immediately be a preposition other than "cu"; AND (2) the noun is not qualified by any other words. Therefore:
Eu lucrez la ziar. = I work at the newspaper.
Eu lucrez la ziarul zilnic. = I work at the daily newspaper.
Am omorât țânțarul cu ziarul. = I have killed the mosquito with the newspaper. (Because "cu" is the exception.)