Le dernier chapitre est plus difficile que le premier.

French makes this kind of comparison with:

• plus = more
• adjective = the quality being compared
• que = than

So:

• plus difficile que = more difficult than

In the full sentence, Le dernier chapitre est plus difficile que le premier, the idea is:

• The last chapter
• is
• more difficult than
• the first one

This same pattern works with many adjectives:

• plus long que = longer than
• plus intéressant que = more interesting than
• plus facile que = easier than

In French, adjective position is not always the same as in English. Many adjectives come after the noun, but some common ones often come before it.

Premier and dernier are very often placed before the noun when they show order in a sequence:

• le premier chapitre = the first chapter
• le dernier chapitre = the last chapter

So le dernier chapitre is the normal word order here.

Because both parts refer to specific things:

• le dernier chapitre = the last chapter
• le premier = the first one

French uses the definite article le just as English uses the.

In the comparison, the second part still needs its article because it means than the first one, not just than first.

Because the noun is understood from the context.

Earlier in the sentence, we already have chapitre, so French can leave it out the second time:

• le dernier chapitre = the last chapter
• le premier = the first one

English does something similar:

• The last chapter is more difficult than the first.

We understand that the first means the first chapter.

Yes. French adjectives normally agree in gender and number with the noun they describe.

Here, chapitre is:

• masculine
• singular

So the adjective is singular too: difficile

A useful detail: difficile has the same form in masculine and feminine singular, so you do not see a spelling change here.

But in the plural, it changes:

• un chapitre difficile = a difficult chapter
• des chapitres difficiles = difficult chapters

Because French often uses être to link a subject to an adjective.

The structure is:

• subject + être + adjective

Here:

• Le dernier chapitre = subject
• est = is
• plus difficile que le premier = more difficult than the first one

Est is the he/she/it is form of être, because le dernier chapitre is singular.

This is an important distinction:

• plus difficile = more difficult
• le plus difficile = the most difficult

So:

• Le dernier chapitre est plus difficile que le premier
  = The last chapter is more difficult than the first

But:

• Le dernier chapitre est le plus difficile
  = The last chapter is the most difficult

The first is a comparison between two things.
The second is a superlative: it says one thing is at the top of the whole group.

They are words of order.

• premier = first
• dernier = last

In this sentence, they identify position in a sequence of chapters:

• le premier = the first chapter
• le dernier chapitre = the last chapter

So they are not just describing the chapters; they are telling you where each one comes in the book.

A careful pronunciation is approximately:

luh der-NYAY sha-PEE-tr eh ploo dee-fee-SEEL kuh luh pruh-MYAY

A more IPA-style version is:

lə dɛʁnje ʃapitʁ ɛ ply difisil kə lə pʁəmje

A few helpful notes:

• dernier sounds roughly like der-NYAY
• chapitre ends with a French tr sound, not a strong English ter
• plus here is usually pronounced like ploo
• premier ends like myay

You do not need perfect pronunciation right away, but recognizing premier, dernier, and plus...que by sound is very useful.