De negende les begint.

Because les is a de-word in Dutch.

In Dutch, singular nouns take either de or het:

• de les = the lesson
• plural: de lessen = the lessons

Since les is a de-word, the article must be de.

Also, when a de-word has an adjective or ordinal before it, that word usually gets -e:

• de negende les

Because it is an ordinal number used before a noun.

In Dutch, ordinals often behave like adjectives when they come before a noun, so they usually take an -e ending:

• de eerste les = the first lesson
• de tweede les = the second lesson
• de negende les = the ninth lesson

So here:

• negen = nine
• negende = ninth

The -e is there because it is directly describing les.

Negende is the ordinal form of negen.

Dutch ordinal numbers are usually formed like this:

• often -de is added
• sometimes -ste is used instead

Examples:

• vier → vierde
• zes → zesde
• negen → negende
• acht → achtste
• twintig → twintigste

A few very common ordinals are irregular:

• een → eerste
• drie → derde

So negende is the normal ordinal form meaning ninth.

It is an ordinal numeral functioning like an adjective.

It tells you which lesson:

• not just any lesson
• specifically the ninth one

So in grammar terms, it modifies les, just like an adjective would.

Because begint is the finite verb, matched to the subject in the present tense.

The infinitive is:

• beginnen = to begin

The present tense forms are:

• ik begin
• jij begint
• hij/zij/het begint
• wij beginnen
• jullie beginnen
• zij beginnen

In De negende les begint, the subject is de negende les, which is singular, so Dutch uses the singular form begint.

It is not really at the end for a special reason here; it is simply in the normal position for a basic Dutch main clause.

The structure is:

• De negende les = subject
• begint = verb

Dutch main clauses usually follow the verb-second rule. In this sentence, the subject comes first, so the verb comes second:

• De negende les begint.

That is completely normal Dutch word order.

If another element came first, the verb would still stay in second position:

• Nu begint de negende les. = Now the ninth lesson begins.

Yes, very often it can.

Dutch simple present can cover meanings that English sometimes expresses in different ways:

• begins
• is beginning
• sometimes even starts

So De negende les begint could be understood as:

• The ninth lesson begins
• The ninth lesson is beginning
• The ninth lesson starts

The exact English translation depends on context.

Yes, both are possible, but beginnen is very common and natural.

You could say:

• De negende les begint.
• De negende les start.

Both are understandable. Begint often feels a bit more neutral and everyday in this kind of sentence.

It is singular.

You can tell because:

• the article is de
• the noun is les, not lessen
• the verb is singular: begint

Compare:

• De negende les begint. = The ninth lesson begins.
• De negende lessen beginnen. = The ninth lessons begin.
  This second one is grammatically possible, but much less likely in normal context.

Roughly, negende sounds like NAY-ghun-duh or NEH-ghun-duh, depending on accent and how approximate you want the English comparison to be.

A few useful points:

• the first syllable has the vowel of negen
• the g is the Dutch g, which is much harsher than English g in many accents
• the final -e is usually a weak uh sound

A broad approximation:

• negende ≈ NAY-ghun-duh

But the Dutch g does not have a perfect English equivalent.

Not exactly in the same form.

De negende les means the ninth lesson, with an ordinal number.

If you wanted something more like Lesson Nine begins as a title or numbered item, Dutch might use a different style, such as:

• Les negen begint.

But in ordinary grammar:

• de negende les = the ninth lesson

So this sentence is most naturally understood as The ninth lesson begins.

Not always, but in this sentence yes, because it is talking about a specific lesson: the ninth lesson.

Without the article, you could sometimes get a more general or stylistically different phrase, but in normal everyday usage:

• de negende les is the standard form for the ninth lesson

So for this sentence, de is the natural and correct choice.