Learn Hardcore French: Je suis fatigué, mais je dois suivre le cours de français. - I am tired, but I have to attend the French class.

In French, states like being tired, hungry, happy, sad are usually expressed with être (to be) + an adjective: je suis fatigué (I am tired).
Fatigué here is an adjective describing your state, not a verb.

J’ai fatigué would be understood as a past-tense verb (I tired [someone/something] out), which is not what you want. So for I am tired, you must say Je suis fatigué.

Does fatigué change if the speaker is a woman?

Yes. Fatigué agrees in gender and number with the person it describes:

Man (singular): je suis fatigué
Woman (singular): je suis fatiguée
Group of men / mixed group: nous sommes fatigués
Group of women: nous sommes fatiguées

The extra e and s are usually silent in speech, but they are required in writing.

Why is there an accent in fatigué, and what happens if I forget it?

The é in fatigué (past participle/adjective of fatiguer) is important:

é is pronounced like the e in they.
Without the accent (fatigue), you get the noun la fatigue (tiredness) or the present tense il/elle fatigue (he/she tires).

So je suis fatigué = I am tired (adjective),
while la fatigue = tiredness (noun).
Dropping the accent is a spelling mistake and can change what word it looks like.

How do you pronounce the whole sentence?

Approximate English-style pronunciation:

Je suis → zhuh swee
fatigué → fa-tee-gay
mais → meh
je dois → zhuh dwah
suivre → sweevr (the re is barely pronounced)
le cours → luh koor (final s is silent)
de → duh
français → frahn-seh (nasal an, final s silent)

Whole sentence:
Zhuh swee fa-tee-gay, meh zhuh dwah sweevr luh koor duh frahn-seh.

What tense is je dois, and what does devoir really mean?

Je dois is the present tense of the verb devoir.
Devoir expresses:

Obligation / necessity: must, have to → je dois suivre = I have to / I must take.
Moral duty: ought to, should in some contexts.
Probability (in other sentences): must, is probably (e.g. il doit être ici = he must be here).

In your sentence it clearly means I have to.

Why is the verb suivre used for “to take a class”? Could I say prendre un cours or assister à un cours?

In French, suivre un cours literally means to follow a course and is the most standard way to say to take a class:

suivre un cours = to be enrolled in it, attend it regularly, follow its content.
prendre un cours is also used, especially for things like prendre des cours de piano, but suivre un cours sounds more academic/formal.
assister à un cours focuses on attending a specific class session (to be present at it).

In your sentence, je dois suivre le cours de français is perfectly natural.

Why is it le cours de français and not le cours français or du français?

French uses de to show what a course is about:

le cours de français = the French course / the course of French (subject).
Saying le cours français would mean the French course in the sense of a course that is French (e.g. a course from France), not “a course on the French language”.
du français after cours (like le cours du français) would sound wrong here; de after cours is the normal way to express the subject matter.

So for school subjects, you typically say un cours de mathématiques, un cours d’histoire, un cours de français, etc.

What’s the difference between cours and classe in this context?

They don’t map perfectly to English:

un cours = a course, a class in the sense of the teaching/lesson or subject.
- suivre un cours de français = to take a French course.
une classe usually means:
- the group of students (our class), or
- the physical classroom in some contexts.

To say take a French class, French normally prefers suivre un cours de français, not suivre une classe de français.

Why is français not capitalized here?

In French:

Nationalities and languages as adjectives or common nouns are not capitalized:
- un cours de français, un professeur anglais, je parle français.
They are capitalized only when they are proper nouns, usually for people or official names:
- un Français, une Française, la République française (styles vary, but the common noun stays lowercase).

Here français is an adjective meaning French (language), so it stays lowercase.

Is the comma before mais necessary in French?

In French, it is very common and stylistically normal to put a comma before mais when it connects two clauses:

Je suis fatigué, mais je dois suivre le cours de français.

You may occasionally see Je suis fatigué mais je dois… without a comma, but the comma is standard and recommended in writing, much more than in everyday English.

Could I replace mais with et or something else?

Mais expresses contrast, like but:

Je suis fatigué, mais je dois suivre le cours… = I’m tired, but I have to…

If you use et (and):

Je suis fatigué et je dois suivre le cours…
This just lists two facts, with much weaker contrast: I’m tired and I have to take the class.

Other possible connectors with nuances:

pourtant / cependant = however, yet (more formal):
Je suis fatigué, pourtant je dois suivre le cours de français.

For normal spoken French, mais is the natural choice.

Could I say Je suis fatigué, mais il faut que je suive le cours de français instead of je dois suivre? Is there a difference?

Yes, you can say that, and it’s correct. The nuance:

Je dois suivre le cours de français
→ direct obligation resting on me: I must / I have to take the class.
Il faut que je suive le cours de français
→ more impersonal: it is necessary that I take the class (it has to be done, I have to do it).

In everyday speech, they’re very close in meaning.
Je dois + infinitive is slightly more direct and simpler; il faut que + subjunctive sounds a bit more formal or impersonal.