Schroef de lamp vast nadat je hem hebt geïnstalleerd.

It is a command: the imperative of schroeven (to screw).

Dutch often makes the imperative with the bare verb stem:

• schroeven → schroef
• lopen → loop
• kijken → kijk

So Schroef de lamp vast means Screw the lamp tight / Fasten the lamp.

Notice that Dutch usually does not need a subject pronoun in a command, just like English often doesn't:

• Open the door.
• Schroef de lamp vast.

Because this is a separable verb: vastschroeven.

In Dutch, many verbs have a main part plus a separable particle. In the dictionary, the verb is written as one word:

• vastschroeven = to screw tight / to fasten with screws

But in a main clause or command, the verb splits:

• Ik schroef de lamp vast.
• Schroef de lamp vast.

So schroef ... vast is the split form of vastschroeven.

Here vast means something like firmly, securely, or fixed in place.

So schroeven by itself is just to screw, but vastschroeven means to screw down, to fasten securely, or to screw tight.

That is why Schroef de lamp vast is stronger and more specific than just Schroef de lamp.

Because nadat introduces a full clause with its own subject and verb:

• nadat je hem hebt geïnstalleerd

Dutch usually uses:

• na
  • noun phrase
• nadat
  • clause

Compare:

• na de installatie = after the installation
• na het installeren = after installing
• nadat je hem hebt geïnstalleerd = after you have installed it

English uses after for both jobs, but Dutch normally makes this distinction.

Because nadat is a subordinating conjunction. In Dutch subordinate clauses, the verb goes to the end.

So the structure is:

• nadat
  • subject + other elements + verb(s)

Here that gives:

• nadat = after
• je = you
• hem = it/him
• hebt geïnstalleerd = have installed

That is why it is:

• nadat je hem hebt geïnstalleerd

and not:

• nadat je hebt hem geïnstalleerd

The pronoun hem comes before the verb cluster, which is normal in Dutch.

Because Dutch very often uses the perfect tense after nadat when one action must be completed before another.

So:

• nadat je hem hebt geïnstalleerd

emphasizes that the installation happens first, and only then do you fasten the lamp.

It is similar to English after you have installed it, although English sometimes also says after you install it. Dutch tends to like the completed form here.

Je is the unstressed form of jij.

In ordinary sentences, especially inside a subordinate clause, je is usually the neutral, natural choice:

• nadat je hem hebt geïnstalleerd

If you used jij, it would sound more emphatic, as if you were stressing you in particular:

• nadat jij hem hebt geïnstalleerd

So the sentence uses je because no special emphasis is needed.

Dutch does not use one single pronoun exactly like English it for all nouns.

Instead, pronouns often follow the noun's grammatical gender/class. Since lamp is a de-word, Dutch commonly uses a pronoun like hem for it.

So:

• de lamp → hem

For English speakers, this feels strange because English would simply say it. In Dutch, objects are often referred to with pronouns that look like him/her/it, depending on the noun.

In modern everyday Dutch, especially in the Netherlands, hem is very common for many inanimate de-words.

The two dots on ï show that the vowels are pronounced separately:

• ge-ïnstalleerd

Without the diaeresis, a learner might try to read ei as one sound. The spelling mark tells you: do not combine these vowels into one unit.

This happens in other Dutch words too, for example:

• beïnvloeden
• coöperatie
• reëel

So geïnstalleerd is just the normal correct spelling of the past participle of installeren.