The /n/ of "en" will sometimes be pronounced closer to the following consonant, becoming a nasal with the same place of articulation as it. So roughly "m" before m, b, p, "ng" before k and g, and just "n" elsewhere. It is always correct to say "n" in any case, but most Norwegian speakers will not notice which pronunciation they use. Note that this is common in quite rapid speech. If you use the other nasals in slow speech, it would sound unnatural, so I advice you to stick to "n" until you develop the fluency needed. Good luck!
The article used with neuter nouns is et, e.g., et hus / huset; et egg / egget.
The article used with masculine nouns is en, e.g., en bil / bilen.
The en article can also be used with feminine nouns, e.g., en seng / sengen. Alternatively, you can use ei as the indefinite article with feminine nouns, e.g., ei jente, and an a ending for the definite form, e.g., jenta (the girl).