Læg mobilen væk, mens vi spiser aftensmad.

Læg is the imperative form of lægge, so it is used for a command: Put ... away.

Just like in English, the subject is usually omitted in commands. So the full idea is really something like (You) put the phone away.

In Danish, the same imperative form can be used whether you are speaking to one person or more than one person.

This is a very common Danish distinction.

Lægge means to lay / to put something down. It usually takes an object: Jeg lægger mobilen på bordet = I put the phone on the table.

Ligge means to lie / to be lying. It does not mean actively placing something: Mobilen ligger på bordet = The phone is lying on the table.

So in this sentence, læg is correct because someone is being told to actively put the phone away.

In Danish, the definite article is often added to the end of the noun.

So:

en mobil = a phone / a mobile
mobilen = the phone

That -en ending is doing the job that the does in English.

In this sentence, mobilen can sound like the phone, but in natural English we might often translate it as your phone, because the context makes that clear.

Yes. Mobil is a very common short form of mobiltelefon.

So:

en mobil = a mobile phone / cell phone
mobilen = the mobile phone / the cell phone

It is completely natural everyday Danish.

Væk means away, but here it is part of the very common expression lægge noget væk, which means to put something away.

So:

læg mobilen væk = put the phone away

This works a bit like an English phrasal verb. The meaning comes from the combination, not just from each word separately.

In Danish, with expressions like lægge ... væk, the object normally comes before the particle væk.

So the natural order is:

læg + object + væk

That gives:

Læg mobilen væk

This is the normal Danish pattern here.

Mens means while. It introduces something that happens at the same time as the main action.

So:

Læg mobilen væk, mens vi spiser aftensmad
= Put the phone away while we eat dinner

A close alternative is imens, which also means while and is often interchangeable in everyday use.

It is not the same as når, which usually means when.

Danish usually uses the simple present where English might use either the simple present or the present progressive.

So:

vi spiser can mean
we eat or we are eating

In this sentence, because of mens, the ongoing meaning is clear: while we are eating dinner

Danish does not need a special progressive form here.

Meal words in Danish often appear without an article after verbs like spise.

For example:

spise morgenmad = eat breakfast / have breakfast
spise frokost = eat lunch / have lunch
spise aftensmad = eat dinner / have dinner

So aftensmad here is perfectly normal without en or -en.

If you were talking about a specific dinner as a noun, you could say aftensmaden.

Because Danish makes compound nouns very freely.

Aftensmad is a compound meaning literally something like evening food, and in normal English that corresponds to dinner / evening meal.

It is formed from aften + a linking -s- + mad.

Writing it as one word is the normal Danish spelling.

Usually, yes. Aftensmad is the normal word for the evening meal, so dinner is the most natural translation in many contexts.

Depending on region, family habits, or style, you may also hear middag used for the main meal, but aftensmad is very common and straightforward.

So for a learner, aftensmad = dinner / evening meal is a very good rule.

Because mens introduces a subordinate clause, and in Danish subordinate clauses do not follow the main-clause verb-second pattern.

So after mens, the normal order is:

subject + verb + object

That is why you get:

mens vi spiser aftensmad

not a verb-first pattern.

Because mens vi spiser aftensmad is a subordinate clause.

A comma before a subordinate clause is very common in Danish, especially in the traditional comma style. You may also sometimes see the sentence written without that comma, depending on the comma system being used.

So the comma here is normal and expected.