På fredag er kokken travl, fordi restauranten er fuld af gæster.

På fredag means on Friday or, very often in everyday Danish, this coming Friday / next Friday depending on context.

Danish often uses på with days when talking about something happening on that day:

• på mandag = on Monday
• på fredag = on Friday

English sometimes says just Friday, but Danish commonly uses på here.

This is because Danish follows the V2 rule in main clauses: the finite verb usually comes in the second position.

In this sentence, På fredag has been placed first for emphasis or time-setting, so the verb er must come next:

• På fredag er kokken travl

If you start with the subject instead, then you get:

• Kokken er travl på fredag

Both are correct, but the word order changes because of the V2 rule.

Kokken means the cook / the chef, while en kok means a cook / a chef.

Danish usually adds the definite article to the end of the noun:

• en kok = a cook
• kokken = the cook

So kokken refers to a specific cook that both speaker and listener can identify.

It can often correspond to both cook and chef in English, depending on context.

• kok = a person who cooks professionally
• In many situations, English might naturally translate it as chef
• In simpler or more literal contexts, cook also works

So the exact English word depends on the situation, but the Danish noun itself is normal and common.

Travl is the common adjective form used with a person:

• Kokken er travl = The cook is busy

You may also see travlt, but that is often used in expressions like:

• Jeg har travlt = I am busy
• Der er travlt = It is busy / things are hectic

So with a noun like kokken, travl is the expected form here.

Because the Danish noun is en restaurant, and when it becomes definite, the ending is added directly:

• en restaurant = a restaurant
• restauranten = the restaurant

The spelling stays based on restaurant, so the definite ending gives restauranten.

Fordi means because. It introduces a reason:

• Kokken er travl, fordi restauranten er fuld af gæster.
• The cook is busy because the restaurant is full of guests.

It links the main idea to the explanation.

After fordi, Danish normally uses subordinate clause word order, which often looks more like English word order:

• fordi restauranten er fuld af gæster

Here the subject restauranten comes before the verb er.

This contrasts with the main clause, where V2 applies:

• På fredag er kokken travl

So the sentence shows two different patterns:

• main clause: verb in second position
• subordinate clause after fordi: subject before verb

Fuld af means full of.

Examples:

• fuld af gæster = full of guests
• fuld af mennesker = full of people
• fuld af problemer = full of problems

It is a very common expression in Danish.

Because fuld af is often followed by an indefinite plural noun when you mean the place is full of some group in general:

• fuld af gæster = full of guests
• fuld af børn = full of children

If you said gæsterne, that would mean the guests, referring to a specific known group. That is possible in the right context, but here the general idea is simply that there are many guests in the restaurant.

Yes.

• en gæst = a guest
• gæster = guests
• gæsten = the guest
• gæsterne = the guests

So af gæster literally means of guests.

Usually no. På fredag normally points to a specific Friday, especially the coming one.

If you want to talk about Fridays in general, Danish would more naturally use something like:

• Om fredagen = on Fridays / on Friday(s)
• Hver fredag = every Friday

So this sentence is most naturally understood as talking about one particular Friday.

Yes, in many situations you can, and it is extremely common.

• Kokken er travl = The cook is busy
• Kokken har travlt = The cook is busy

Both are natural, but have travlt is a very frequent Danish way to express being busy. The version in your sentence is still correct and clear.

Danish uses commas to mark clause boundaries, and a subordinate clause introduced by fordi is normally separated by a comma:

• På fredag er kokken travl, fordi restauranten er fuld af gæster.

This is standard Danish punctuation.