Magistra dicit auctorem naturam hominum bene describere.

Because after dicit meaning says, Latin often uses an indirect statement construction.

In this construction:

• the subject of the reported statement goes into the accusative
• the verb of the reported statement goes into the infinitive

So instead of saying something like the author describes..., Latin says:

• auctorem = the author as the subject of the indirect statement, but in the accusative
• describere = to describe

So dicit auctorem describere means she says that the author describes.

The main verb is dicit = says.

Everything after that, auctorem naturam hominum bene describere, is what the teacher says.

So the sentence is built like this:

• Magistra = the teacher
• dicit = says
• auctorem naturam hominum bene describere = that the author describes human nature well

The one doing the describing is auctorem.

Even though auctorem is accusative, it is still the logical subject of describere inside the indirect statement.

So:

• Magistra dicit = the teacher says
• auctorem describere = that the author is describing

This is one of the most important things to get used to in Latin: in an indirect statement, the subject appears in the accusative.

Because Latin usually expresses reported statements after verbs like dicit, putat, scit, audit, and similar verbs with an accusative + infinitive construction.

So English says:

• The teacher says that the author describes human nature well

But Latin says more literally:

• The teacher says the author to describe human nature well

Of course that literal English sounds wrong, but it helps show the Latin structure.

So describere is infinitive because it belongs to the reported statement after dicit.

Naturam is accusative singular.

Its job is to be the direct object of describere.

So:

• auctorem = the subject of the indirect statement
• describere = to describe
• naturam = nature, the thing being described

In other words, the author is describing nature.

Hominum is the genitive plural of homo, meaning human being, man, or person depending on context.

Here it depends on naturam and means:

• naturam hominum = the nature of human beings / human nature

The genitive often shows possession or close relationship, so hominum tells us whose nature is being described.

Latin often uses a noun in the genitive where English might prefer an adjective.

So:

• naturam hominum literally = the nature of people
• natural English translation = human nature

Both ideas are the same, but Latin expresses it with nature + of people.

Bene modifies describere.

It is an adverb meaning well, so it tells us how the author describes human nature.

So:

• describere = to describe
• bene describere = to describe well

It does not describe magistra, auctorem, or naturam. It describes the action.

Yes. Magistra is the subject of the main verb dicit.

So:

• Magistra = the teacher
• dicit = says

This is a nominative singular feminine noun, so it means the female teacher or simply the teacher, if the feminine is clear from context.

In classical Latin, after a verb like dicit, the normal way to express that... in a statement is the accusative + infinitive construction, not a quod clause.

So Latin prefers:

• Magistra dicit auctorem naturam hominum bene describere

rather than a clause introduced by quod.

For learners, it is best to recognize this pattern:

• verb of saying/thinking/perceiving
• accusative subject
• infinitive verb

That pattern is extremely common.

It can often be translated in more than one way depending on context.

Latin infinitives in indirect statement do not always map neatly onto one English tense. Here, describere could be understood as:

• describes
• is describing

In a simple sentence like this, English usually prefers describes:

• The teacher says that the author describes human nature well

But context could sometimes make a more progressive translation possible.

A helpful way to break it down is this:

• Magistra = subject
• dicit = main verb
• auctorem = subject of the indirect statement, in the accusative
• naturam hominum = object phrase, human nature
• bene = adverb, well
• describere = infinitive verb of the indirect statement

So the sentence follows this pattern:

subject + verb of saying + accusative subject + object + adverb + infinitive

That is a very common Latin sentence pattern.