"en"used in common gender,and "ett"is for neuter gender,I just know a little denmark,but they're quite similar...XD

All Swedish nouns are either of general gender or neuter gender. "En" is an indefinite article of general gender. "Ett" is an indefinite article of neuter gender. For example, en bil = a car, en gata = a street, ett hus= a house, ett rum=a room. When we add these articles to the end of words, they become definite articles.(Note that "ett" as a definite article has only one "t"). For example, bilen=the car, gatan=the street, huset=the house, rumet=the room. When a noun ends in a vowel, we add only "n" or "t": en kvinna - kvinnan, ett hjarta - hjartat. Nouns of general gender ending in "el" or "er" have only "n" at the end: en nyckel - nyckeln, en dotter - dottern. Nouns of both genders ending in "en" and nouns of neuter ending in "el" and "er" omit "e" before the article. en oken-oknen, ett exempel - exemplet.

This question was recently asked by another person. But you might have missed it so here is the link: http://www.italki.com/answers/question/95970.htm The answers are in Swedish though so if you might want to use an online translator if you aren't fluent in Swedish.