Mercator panem venditurus ad forum festinat.

The main verb is festinat.

It is:

• present tense
• active voice
• indicative mood
• 3rd person singular

So festinat means he/she hurries or is hurrying.

Everything else in the sentence is built around that main idea: the merchant hurries.

Venditurus is the future active participle of vendo, vendere (to sell).

Here it means something like:

• about to sell
• going to sell
• intending to sell

So Mercator panem venditurus ad forum festinat literally has the sense:

The merchant, intending to sell bread, hurries to the forum.

In smoother English, you might say:

The merchant hurries to the forum to sell bread.

It is a participle, which means it is a verbal adjective.

That means it has a double nature:

• like a verb, it can still take an object: panem
• like an adjective, it agrees with the noun it describes: mercator

So venditurus is not the main finite verb of the sentence. It describes mercator while also carrying verbal meaning.

Panem is the direct object of venditurus.

Even though venditurus is a participle, it still keeps the verbal force of vendo and can govern an object, just as vendit would.

So:

• panis = bread
• panem = bread as the thing being sold

In other words, the merchant is about to sell bread.

Because it agrees with mercator.

Mercator is:

• masculine
• singular
• nominative

So the participle describing it must also be:

• masculine
• singular
• nominative

That gives venditurus.

If the subject were feminine, you would expect venditura instead.

Mercator is nominative singular, and it is the subject of festinat.

You can tell from its role in the sentence:

• mercator = the merchant
• festinat = hurries

So the merchant hurries.

Also, mercator is a third-declension noun, which is why its nominative singular does not end in -us like many second-declension masculine nouns do.

Ad with the accusative often shows motion toward a place.

So:

• ad forum = to the forum

This fits the verb festinat, because hurrying usually involves movement toward a destination.

Also note that forum is in the accusative singular after ad.

Because forum is not one of the special place words that commonly omit a preposition for motion toward.

Latin often says:

• Romam = to Rome
• domum = homeward / to home

But with an ordinary noun like forum, Latin normally uses a preposition:

• ad forum = to the forum

So ad is the normal and expected choice here.

Latin word order is much more flexible than English word order because Latin endings show the grammatical relationships.

This sentence is arranged as:

• Mercator = subject
• panem = object
• venditurus = participle describing the subject
• ad forum = destination
• festinat = main verb

English usually needs a more fixed order, so we might say:

The merchant hurries to the forum to sell bread.

Latin can move these parts around more freely without losing the basic meaning, though different orders can create slightly different emphasis.

No. Latin has no articles like English the or a/an.

So mercator can mean:

• the merchant
• a merchant

And forum can mean:

• the forum
• a forum

Context decides which English article is best in translation.

Here it mainly expresses intention/purpose.

Formally, venditurus is a future participle, but in this sentence the most natural sense is not just will sell later. It is more specifically:

the merchant hurries to the forum with the intention of selling bread

So in idiomatic English, it is often best translated with a purpose phrase:

to sell bread

That is why the sentence sounds more natural in English as:

The merchant hurries to the forum to sell bread.