Ubi racemi collecti sunt, colona eos ad torcular portari iubet.

Because ubi can be used in two different ways:

• as an adverb of place: where
• as a temporal conjunction: when, once

In this sentence, ubi racemi collecti sunt introduces the time at which the next action happens, so ubi is temporal: when or once.

A good way to feel the difference is this:

• Ubi est torcular? = Where is the press?
• Ubi racemi collecti sunt... = When the grape-clusters have been gathered...

Racemi is nominative plural masculine of racemus.

Here it is the subject of collecti sunt, so it means the clusters / bunches. In this context it usually means bunches of grapes or grape-clusters.

You can also see that it must be plural because:

• collecti is plural
• sunt is plural
• eos later refers back to it in the plural

Collecti sunt is the perfect passive indicative, 3rd person plural, from colligo, colligere, collegi, collectus.

It is made of:

• collecti = the perfect passive participle
• sunt = the auxiliary verb are/have been

Literally, it means have been gathered.

Because collecti is a participle, it agrees with racemi in:

• gender: masculine
• number: plural
• case: nominative

So collecti matches racemi exactly.

Either can be correct, depending on context.

The Latin perfect often corresponds to either:

• English present perfect: have been gathered
• English simple past: were gathered

In a sentence like this, English often sounds most natural with:

• when the bunches have been gathered
• once the bunches have been gathered
• sometimes simply when the bunches were gathered

The important idea is that the gathering is completed before the ordering happens.

Yes. Colona is nominative singular, and it is the subject of iubet.

So the basic structure of the main clause is:

• colona = subject
• iubet = verb

A learner may expect colonus, which is the masculine form. But colona is feminine, so the sentence is talking about a female farmer / settler.

Eos is a pronoun referring back to racemi.

It is:

• accusative plural masculine
• meaning them

Latin often uses a pronoun like this instead of repeating the noun. So rather than repeating racemos, the sentence uses eos.

It agrees with racemi in:

• gender: masculine
• number: plural

but its case is accusative because of its role in the main clause / infinitive construction.

Because iubet commonly takes an accusative + infinitive construction.

So:

• colona eos ad torcular portari iubet

means literally something like:

• the farmer orders them to be carried to the press

Here:

• eos is the accusative noun/pronoun linked with the infinitive
• portari is the infinitive

English often uses orders that they be carried, but Latin usually prefers this infinitive construction instead of a separate finite clause.

Portari is the present passive infinitive of porto.

It is passive because the sentence focuses on what happens to the grape-clusters: they are carried.

If Latin used the active infinitive, we would need to say who is carrying them. For example:

• colona servos eos ad torcular portare iubet
  = the farmer orders the slaves to carry them to the press

But in your sentence, the carriers are not named, so the passive is a neat and natural choice:

• eos ... portari iubet = orders them to be carried

Ad takes the accusative and usually means to, toward, or up to.

Since the grape-clusters are being moved in the direction of the press, ad is exactly what you would expect:

• ad torcular = to the press

Torcular is a neuter noun, and in the singular its nominative and accusative forms look the same, so after ad it is accusative singular.

A torcular is a press, especially one used for pressing grapes or olives.

In this sentence, because racemi are grape-clusters, torcular is naturally understood as a wine press or grape press.

So ad torcular means not just to a machine, but specifically to the place where the grapes will be pressed.

The sentence is arranged very naturally for Latin:

• Ubi racemi collecti sunt, = background/time first
• colona = subject
• eos ad torcular portari = what is ordered
• iubet = main verb at the end

A more mechanical layout would be:

• Colona iubet eos ad torcular portari, ubi racemi collecti sunt

but that is much less natural.

Latin often:

• puts the time clause first
• leaves the main verb until the end
• uses word order for emphasis and flow, not just grammar

The endings tell you the grammar; the order helps shape the sentence stylistically.