Hun låser døren.

Låser is the present tense form of the verb låse (infinitive å låse), which means to lock. In Norwegian Bokmål you form the present by adding -r to the infinitive:
– å låse → låser

Norwegian uses an enclitic (attached) definite article. Instead of a separate word like English the, you add -en for common-gender nouns:
– en dør (a door) → døren (the door)

Dør is a common-gender noun in Bokmål (a merger of traditional masculine and feminine). Common-gender singular takes en in the indefinite form and -en in the definite:
– Indefinite: en dør
– Definite: døren

– å is pronounced like the aw in law (long oː).
– ø is similar to the vowel in English hurt (without the r).
Together: låser ≈ “LAW-ser”, døren ≈ “DUR-en.”

Norwegian does not have a separate progressive tense. The simple present covers both English “she locks” and “she is locking.”
– Hun låser døren. can mean either “She locks the door” or “She is locking the door.”

No. Norwegian verbs are unchanged for person and number in the present tense:
– Jeg låser (I lock)
– Du låser (you lock)
– Han låser, Hun låser (he/she locks)
– Vi låser (we lock)
– De låser (they lock)

You use the past tense låste (remove -r, add -te):
– Hun låste døren.

The opposite is å låse opp (“to unlock”). In the present tense:
– Hun låser opp døren. (She unlocks the door.)