Ik leg mijn bril op het bureau.

The verb is leggen (to lay / to put something down). Dutch present tense conjugation:

• ik leg – I lay / I put
• jij/u legt – you lay / you put
• hij/zij/het legt – he/she/it lays / puts
• wij leggen – we lay / put
• jullie leggen – you (plural) lay / put
• zij leggen – they lay / put

In Dutch, the ik form usually drops the final -en, so leggen → leg.

So Ik leg is simply I lay / I put.
Leggen is the infinitive (to lay), and legt is the you/he/she/it form.

Both can translate as to put, but there is a nuance:

• leggen – to lay something down flat (on its side or lying).
• zetten – to set something upright (standing).

With a bril (pair of glasses), speakers often imagine it lying flat, so leggen is natural:

• Ik leg mijn bril op het bureau. – I put my glasses (lying flat) on the desk.

In everyday speech, many people also say:

• Ik zet mijn bril op het bureau.

That’s not wrong in colloquial Dutch, but leggen fits the traditional flat-vs-upright distinction better.

Dutch treats a pair of glasses as one object:

• de bril – the pair of glasses
• mijn bril – my glasses
• een bril – a pair of glasses

Plural brillen exists, but it means multiple pairs:

• Ik heb drie brillen. – I have three pairs of glasses.

So Ik leg mijn bril op het bureau. literally: I lay my pair-of-glasses on the desk, which we translate naturally as my glasses.

The preposition depends on the spatial relationship:

• op – on (top of) a surface
  
  • op het bureau – on the desk (on its top surface)
• in – in / inside
  
  • in het bureau – inside the desk (e.g. in a drawer)
• aan – connected to or at the side of something
  
  • aan het bureau zitten – to sit at the desk

You are putting the glasses on top of the desk, so op het bureau is correct.

Every Dutch noun has a grammatical gender: de-words or het-words.

• bureau (desk) is a het-word: het bureau.
• Plural is de bureaus (all plurals take de).

Unfortunately, you mostly have to memorize whether a noun is de or het. There are patterns, but bureau is just one to learn as het bureau.

It can mean both, depending on context:

1. Physical piece of furniture – desk

   • Ik leg mijn bril op het bureau. – on the desk.

2. Organization / office (company, government office, agency)

   • Een reisbureau – a travel agency
   • Het bureau van de burgemeester – the mayor’s office (as an organization)

In your sentence, because something is physically on it, it clearly means desk.

Yes, the sentence is grammatically fine:

• Ik leg de bril op het bureau.

However, the meaning changes slightly:

• mijn bril – specifically my glasses.
• de bril – the glasses (some specific pair known from context, not necessarily mine).

In everyday speech, if you mean your own glasses, mijn bril is the most natural.

No. Dutch is not a “pro-drop” language. You must include the subject pronoun in normal sentences:

• ✅ Ik leg mijn bril op het bureau.
• ❌ Leg mijn bril op het bureau. – This sounds like an imperative (a command: Put my glasses on the desk.), not a normal statement.

For a regular statement meaning I put my glasses on the desk, you always keep ik.

The main rule for Dutch main clauses:

• The finite verb (here: leg) is in second position.

In your sentence:

1. Ik – first element (subject)
2. leg – verb in second position
3. mijn bril op het bureau – rest of the sentence

So you cannot move words in front of leg without changing the structure. For example:

• ❌ Ik op het bureau mijn bril leg. – incorrect word order.
• ✅ Morgen leg ik mijn bril op het bureau.
  Here, Morgen is first, so leg still comes second, followed by ik.

The verb leggen is a regular weak verb. Past tense:

• ik/jij/hij legde
• wij/jullie/zij legden

So:

• Ik leg mijn bril op het bureau. – I put / am putting my glasses on the desk.
• Ik legde mijn bril op het bureau. – I put my glasses on the desk. (past)

Everything else in the sentence (mijn bril op het bureau) stays the same.