Voordat ik ga slapen, ruim ik mijn boek op.

Voordat means before when it introduces a whole clause.

So in:

• Voordat ik ga slapen = Before I go to sleep

Dutch uses voordat when what follows has its own subject and verb:

• voordat ik ga slapen
• voordat hij vertrekt
• voordat we eten

A useful comparison:

• voor het eten = before dinner / before eating
• voordat we eten = before we eat

So voordat is the conjunction used for before + clause.

Because ik ga slapen means I am going to sleep / I’m going to bed / I’m about to sleep, while ik slaap means I sleep / I am sleeping.

That is an important difference:

• Voordat ik ga slapen = before I go to sleep
• Voordat ik slaap would sound more like before I sleep, which is not the usual idea here

Dutch often uses gaan + infinitive in expressions about beginning an action, especially with sleeping:

• Ik ga slapen. = I’m going to sleep.
• Het kind gaat slapen. = The child is going to sleep.

So ga slapen is the natural expression here.

Because voordat introduces a subordinate clause, and in modern Dutch the finite verb usually goes toward the end of the clause, but with a verb combination like gaan slapen, both verbs stay together in the usual order:

• ik ga slapen

This is the normal, modern pattern.

You may sometimes see more old-fashioned or formal-looking end clusters in Dutch grammar discussions, but for everyday Dutch:

• voordat ik ga slapen is the natural version

So this is just the standard way to say it.

Because the sentence begins with another element: the clause Voordat ik ga slapen.

In Dutch main clauses, the conjugated verb normally comes in second position. This is often called the V2 rule.

So the structure is:

1. Voordat ik ga slapen
2. ruim
3. ik mijn boek op

That gives:

• Voordat ik ga slapen, ruim ik mijn boek op.

If the sentence started directly with the subject, then you would get:

• Ik ruim mijn boek op voordat ik ga slapen.

Both are correct. The first one just puts more emphasis on the time phrase before I go to sleep.

Because opruimen is a separable verb.

The full verb is:

• opruimen = to tidy up / to put away / to clear away

In a main clause, Dutch usually splits separable verbs:

• Ik ruim mijn boek op.

Here:

• ruim = the conjugated verb part
• op = the separated prefix

Compare:

• Ik ruim de kamer op.
• Hij belt me op. from opbellen
• Wij staan vroeg op. from opstaan

But in infinitives or subordinate-style verb groups, the verb often stays together:

• Ik wil mijn boek opruimen.
• ... omdat ik mijn boek opruim is different, because now it is a finite form, not the infinitive

So op goes at the end because that is how separable verbs work in a main clause.

Here opruimen means something like:

• put away
• tidy away
• clear away

So Ik ruim mijn boek op means that the speaker is putting the book back in its proper place.

A small nuance:

• opruimen often suggests returning something to order
• with a single book, English might more naturally say I put my book away

So the Dutch sentence is understandable, but depending on context, other Dutch verbs could also be natural, such as:

• Ik leg mijn boek weg. = I put my book away.
• Ik ruim mijn spullen op. = I tidy up my things.

With boek, opruimen is possible, but wegleggen may sound a bit more specifically like physically putting the book aside.

Both are possible, but they mean slightly different things.

• mijn boek = my book
• het boek = the book

Using mijn boek makes it clear that it is the speaker’s own book. Dutch uses possessives in much the same way English does here.

So:

• Ik ruim mijn boek op. = I put away my book.
• Ik ruim het boek op. = I put away the book.

The choice depends on what meaning you want.

Yes, normally you put a comma after an initial subordinate clause like this.

So the standard punctuation is:

• Voordat ik ga slapen, ruim ik mijn boek op.

That comma helps mark the boundary between:

• the time clause: Voordat ik ga slapen
• the main clause: ruim ik mijn boek op

In short: yes, this comma is standard and expected.

Yes. That is also correct.

Compare:

• Voordat ik ga slapen, ruim ik mijn boek op.
• Ik ruim mijn boek op voordat ik ga slapen.

The difference is mainly about emphasis and information flow:

• Starting with Voordat ik ga slapen emphasizes the time frame first.
• Starting with Ik ruim mijn boek op emphasizes the action first.

English works similarly:

• Before I go to sleep, I put my book away.
• I put my book away before I go to sleep.

Not in this sentence.

Use voordat before a clause with a subject and verb:

• voordat ik ga slapen
• voordat hij vertrekt

Use voor before a noun or noun phrase:

• voor het slapengaan = before going to sleep
• voor bedtijd = before bedtime

So these are correct:

• Voordat ik ga slapen, ruim ik mijn boek op.
• Voor het slapengaan ruim ik mijn boek op.

But voor ik ga slapen is a different matter: in some varieties of Dutch, especially in Belgium and in some informal usage, voor ik ga slapen can occur, but for learners, voordat is the safest standard choice here.

Yes, the grammar is correct and the meaning is clear.

The only small point is vocabulary choice: with boek, many speakers might more naturally say:

• Voordat ik ga slapen, leg ik mijn boek weg.
• Voordat ik ga slapen, berg ik mijn boek op.

That is because een boek wegleggen can sound more specific for putting a book aside or back.

Still, mijn boek opruimen is understandable and grammatically fine, especially if the idea is part of tidying up.

So:

• Grammatically correct? Yes.
• Perfectly understandable? Yes.
• Most idiomatic in every context? Not always; sometimes wegleggen may sound more natural.