Frater autem sero surgit, quia nocte non bene dormivit.

Because autem is usually postpositive in Latin. That means it normally comes second in its clause, not first. So Frater autem... is the expected order.

It often means however, but, or on the other hand.

Not exactly.

• sed is the more direct, stronger word for but
• autem is often a little softer, more like however or meanwhile

So autem often links the sentence to something previous with a mild contrast.

Latin often leaves out subject pronouns when they are not needed. The verb ending already tells you the person and number.

• surgit = he/she/it gets up, rises, or is getting up
• dormivit = he/she/it slept or has slept

Since frater is already there as the subject, adding is (he) would be unnecessary.

We know from both form and sense.

• frater is in the nominative singular, the normal case for the subject
• surgit is third person singular, so it matches frater

Also, Latin has no word for the or a. So frater can mean brother, a brother, or the brother, depending on context.

Sero is an adverb, meaning late. Because it is an adverb, it does not agree with frater in gender, number, or case.

Compare:

• serus frater = a late brother or a slow brother depending on context, where serus is an adjective
• sero surgit = he gets up late, where sero is an adverb

So here sero describes how he gets up, not what kind of brother he is.

Because the two actions are being viewed differently.

• surgit describes the main action: he gets up / is getting up
• dormivit describes an action already completed before that: he slept / has slept

This is very natural. In English we also say things like He is getting up late because he slept badly. The getting up is the present action; the bad sleeping happened earlier.

Dormivit is:

• third person singular
• perfect
• active
• indicative

from dormire, meaning to sleep.

So it means he/she/it slept or sometimes has slept, depending on context.

Because Latin often uses the ablative of time when without a preposition.

So:

• nocte = at night / during the night

English usually needs a preposition, but Latin often does not. This is especially common with expressions of time.

Nocte is ablative singular of nox, noctis, meaning night.

Here it is ablative because it expresses time when: at night or during the night.

Because quia usually introduces a real cause: because.

When Latin presents the reason as a straightforward fact, it normally uses the indicative, as in:

• quia nocte non bene dormivit = because he did not sleep well at night

At a more advanced level, you may sometimes meet different constructions, but for a learner the main rule is:

• quia + indicative = because

Latin can certainly use words meaning badly, but non bene is a very ordinary and clear way to say not well.

• bene = well
• non = not

So non bene dormivit means literally he did not sleep well.

Yes, Latin word order is fairly flexible because the endings do a lot of the grammatical work.

For example, the sentence could be rearranged in various ways without changing the basic meaning. But some words still have preferences:

• autem usually stays in second position
• the given order is natural and straightforward

So Latin word order is flexible, but not random.

Yes. Latin can put the because clause first if the writer wants.

For example:

• Quia nocte non bene dormivit, frater autem sero surgit.

That still means the same basic thing. The difference is mainly one of emphasis or style. Putting the quia clause first brings the reason to the front.