Pater dicit se quinque libros et sex epistulas cras ad forum portaturum esse, si via tuta erit.

Se is a reflexive pronoun. It refers back to the subject of the main verb, which is pater.

So:

• Pater dicit se ... portaturum esse = Father says that he ... will carry
• Here, he means father himself

If Latin used eum, that would usually mean some other male person, not the father.

So se shows that the person who is speaking in the indirect statement is the same person as the subject of dicit.

This is an indirect statement (also called an accusative-and-infinitive construction).

After verbs of saying, thinking, knowing, hearing, and so on, Latin often uses:

• accusative subject
  • infinitive

Here:

• se = the subject of the indirect statement, in the accusative
• portaturum esse = the infinitive part, meaning to be going to carry / would carry

So the structure is:

• Pater dicit
• se quinque libros et sex epistulas cras ad forum portaturum esse

Literally:
Father says himself to be going to carry five books and six letters to the forum tomorrow.

More natural English:
Father says that he will carry five books and six letters to the forum tomorrow.

Because Latin wants to show future time inside the indirect statement.

• portare = to carry
• portaturum esse = to be about to carry / to be going to carry / to carry in the future

Since the action of carrying will happen tomorrow (cras), Latin uses the future infinitive.

The future infinitive is formed with:

• the future active participle: portaturus, -a, -um
• plus esse

So:

• portaturum esse = to be going to carry (masculine singular form here)

Because it agrees with se, which refers to pater.

The future active participle must agree with the subject of the infinitive in:

• gender
• number
• sometimes it reflects the accusative subject in indirect statement, but the participle itself appears in the accusative form used with esse

Since pater is:

• masculine
• singular

the participle is portaturum.

If the subject were feminine singular, it would be portaturam.
If it were masculine plural, it would be portaturos.

They are the direct objects of portaturum esse.

The verb porto takes a direct object in the accusative:

• libros = books
• epistulas = letters

So:

• quinque libros = five books
• sex epistulas = six letters

Both are things that father will carry, so both are accusative.

Because quinque and sex are numerals that are normally indeclinable in Latin.

That means their forms stay the same regardless of case.

So:

• quinque libri = five books
• quinque libros = five books
• sex epistulae = six letters
• sex epistulas = six letters

The nouns change case, but quinque and sex do not.

Because ad with the accusative expresses motion toward a place.

So:

• ad forum = to the forum

This is different from a phrase that simply describes location:

• in foro = in the forum / at the forum

Since the father is carrying the books and letters to the forum, Latin uses ad forum.

Yes, cras could go in other places. Latin word order is much more flexible than English word order.

Here it appears in:

• se quinque libros et sex epistulas cras ad forum portaturum esse

But Latin could also say things like:

• se cras quinque libros et sex epistulas ad forum portaturum esse
• se quinque libros et sex epistulas ad forum cras portaturum esse

All of these can mean basically the same thing.

The position of cras may affect emphasis or rhythm, but not the core meaning. In this sentence, it naturally goes with the future idea: the carrying will happen tomorrow.

Because the sentence is talking about a future condition.

• si = if
• via tuta erit = the road will be safe

Latin often uses the future tense in both parts of a future condition:

• Pater dicit ... portaturum esse, si via tuta erit

Literally:
Father says that he will carry ... if the road will be safe.

But in natural English, we usually say:

Father says that he will carry ... if the road is safe.

So Latin erit is normal here, even though English usually uses the present tense in the if clause.

Via means road or way. It is a feminine noun.

So the adjective describing it must also be feminine:

• via tuta = a safe road / the road is safe

Here:

• via = feminine singular nominative
• tuta = feminine singular nominative, agreeing with via

Then erit means will be, so:

• via tuta erit = the road will be safe

Because Latin usually does not use a word equivalent to English that in indirect statement after verbs like say, think, know, and hear.

English says:

• Father says that he will carry ...

Latin instead uses the accusative-and-infinitive construction:

• Pater dicit se ... portaturum esse

So the idea of English that is built into the grammar of the indirect statement rather than expressed by a separate word.

Yes. The Latin present tense often covers both:

• simple present: says
• progressive present: is saying

So pater dicit could mean:

• Father says
• Father is saying

Context decides which sounds better in English. In many textbook sentences, says is the most natural translation.

A useful way to break it up is this:

• Pater dicit = main clause: Father says
• se ... portaturum esse = indirect statement: that he will carry
• quinque libros et sex epistulas = objects: five books and six letters
• cras = time: tomorrow
• ad forum = destination: to the forum
• si via tuta erit = condition: if the road is safe / will be safe

So the sentence works as:

Father says [that] he will carry five books and six letters to the forum tomorrow, if the road is safe.

That is the main grammatical pattern to notice: verb of saying + accusative subject + infinitive, followed by the condition.