Learn Hardcore Portuguese (Brazil): Eu tenho aula hoje.

In Brazilian Portuguese, aula is a feminine noun meaning “class” or “lesson.” It refers to a scheduled teaching session, like a school or university class.

Why is there no article (like uma or a) before aula?

When you talk about having classes in general—without specifying one particular lesson—Portuguese often omits the indefinite article.
Compare:
• Tenho aula hoje. (I have class today.) – general, any class scheduled.
• Tenho uma aula hoje. (I have one class today.) – emphasizes “one” specific class.

Is the pronoun Eu necessary? Can I just say Tenho aula hoje?

You can omit Eu because Portuguese verbs are conjugated to show who the subject is.
• Tenho aula hoje. is perfectly natural in conversation.
Use Eu only if you want to add emphasis or avoid ambiguity:
• Eu tenho aula hoje, mas ele não tem.

Can I move hoje to the beginning? For example, Hoje tenho aula?

Yes. Adverbs of time like hoje can appear at the start, middle, or end of a sentence. All are correct and common:
• Hoje tenho aula.
• Tenho aula hoje.
• Tenho hoje aula. (less common, sounds a bit formal or poetic)

How do I make this sentence negative?

Insert não immediately before the verb:
• Eu não tenho aula hoje. (I don’t have class today.)

How do I ask “Do you have class today?” in Portuguese?

You can simply use rising intonation or question marks:
• Você tem aula hoje?
Or drop the pronoun for a more informal tone:
• Tem aula hoje?

What’s the difference between tenho aula hoje and vou ter aula hoje?

• Tenho aula hoje. uses the present tense to express a scheduled event (common in Portuguese).
• Vou ter aula hoje. uses the periphrastic future (ir + infinitive) to emphasize that the class will happen later. Both are correct, but the simple present is more idiomatic for timetables.

Could I say Eu estou tendo aula hoje to mean “I am having class today”?

Technically yes—estar + gerúndio forms the present continuous. But Brazilians rarely say estou tendo aula hoje unless they mean “I’m in the middle of a class right now.” For scheduled classes, stick with Tenho aula hoje.