Adjective or adverb
In «the tired dog slept peacefully», tired describes the dog and is an , while peacefully describes how it slept and is an . Ask what the word describes: a thing, or an action.
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An describes a (the tired dog), an describes a (slept peacefully). Ask what the word describes to tell them apart.
Describes a thing: adjective. Describes an action: adverb.
Do not move the verb
Norwegian puts the second: «I går gikk vi på kino.» English keeps subject before verb: «Yesterday we went to the cinema.» The Norwegian pattern transferred into English is one of the most common mistakes at this level.
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English keeps subject before even after a time phrase: «Yesterday we went to the cinema». Moving the verb to second place is a Norwegian pattern that does not transfer.
Start with the time phrase if you like, but keep subject before verb.
An describes a : the tired dog. An describes a and often ends in ly: she closed the door quickly. Knowing which is which matters because English places them differently, and because a wrong form is one of the errors that stands out most to a reader.
English normally keeps the order subject, , object: «Yesterday we visited the museum», not «Yesterday visited we the museum». Norwegian allows the verb to move to second place, and that is exactly why Norwegian learners get this wrong. Pronunciation also varies between British and , and both are correct within their own variety.