Nonnulli discipuli ad forum oratorem auditum eunt.

Yes, it is built from non + nulli, literally not none, but in actual Latin it means some or several.

So nonnulli discipuli means some students or several students.

This is a very common Latin way of expressing an indefinite plural idea.

Discipuli is the subject of eunt.

• discipulus = student
• discipuli = students or of the student, depending on context

Here it must be nominative plural because:

• the verb eunt means they go
• the people doing the action are the students

So nonnulli discipuli = some students.

Ad takes the accusative case and usually shows motion toward a place.

So:

• ad forum = to the forum

Here forum is accusative singular. Since forum is a neuter second-declension noun, its nominative and accusative singular look the same, so forum can be either form depending on context. After ad, it must be accusative.

Oratorem is the direct object of auditum.

The idea is:

• orator = speaker / orator
• oratorem audire = to hear the speaker

Even though auditum is not a normal finite verb, it still keeps its object in the accusative. So oratorem is accusative because it is the person being heard.

Auditum is the supine of audio.

In this sentence, it is the accusative supine, which is often used after a verb of motion to express purpose.

So:

• eunt = they go
• auditum = to hear

That means:

• oratorem auditum eunt = they go to hear the speaker

This is a standard Latin construction: verb of motion + supine in -um = go/come/send ... to do something

Because after verbs of motion, Latin often uses the supine in -um to express purpose.

So English says:

• they go to hear the speaker

But Latin often says:

• eunt oratorem auditum

A learner might expect an infinitive like audire, but the infinitive is not the normal classical construction here. The supine is a special idiomatic way to say in order to hear after words like go, come, send, and so on.

No. Auditum does not agree with oratorem.

That is important because it may look as if it could be some kind of adjective or participle, but here it is a supine, not an agreeing adjective.

So:

• oratorem = accusative singular masculine, the object
• auditum = supine form, expressing purpose

They belong together in meaning, but not by agreement.

Eunt is:

• present tense
• active voice
• indicative mood
• third person plural

from the irregular verb eo, ire = to go

So eunt means they go.

It matches nonnulli discipuli, which is plural.

Latin word order is much more flexible than English word order because Latin shows grammatical relationships mostly through endings, not just position.

This sentence could be rearranged in other ways and still mean the same thing, for example:

• Nonnulli discipuli ad forum eunt oratorem auditum
• Ad forum nonnulli discipuli oratorem auditum eunt

The original order is perfectly natural. Latin often places the main verb at or near the end, and it can keep related ideas together, such as oratorem auditum.

So the learner should not expect Latin to follow English word order closely.