Iter longum est, et nos in oppidum festinamus.

Because iter is a neuter noun.

• iter = journey, route, march
• It is nominative singular neuter
• The adjective must agree with it in gender, number, and case

So:

• iter longum est = the journey is long

If the noun were masculine, you might expect longus, but iter is neuter, so Latin uses longum.

Iter is nominative singular.

It is the subject of est, so Latin puts it in the nominative case:

• iter = the journey
• est = is

So literally: the journey is long.

In many Latin sentences, especially with simple statements, forms of to be are often expressed clearly, as here:

• iter longum est = the journey is long

Latin can sometimes omit forms of esse in certain styles, especially poetry or very compressed prose, but in normal beginner-style prose, including est is standard and helpful.

So here est is simply the normal verb: is.

Yes. The ending -mus in festinamus already tells you the subject is we.

So Latin could simply say:

• et in oppidum festinamus

and it would still mean and we hurry to the town.

When nos is included, it often adds emphasis or clarity:

• nos = we, especially we ourselves or we in particular

So the sentence may suggest a bit of stress on we:

• and we are hurrying into the town

Because in changes meaning depending on the case that follows it.

• in + accusative = into / to / toward a place, showing motion
• in + ablative = in / on a place, showing location

Here the verb festinamus involves movement, so Latin uses the accusative:

• in oppidum = into the town / to the town

Compare:

• in oppidum festinamus = we hurry into the town
• in oppido sumus = we are in the town

Oppidum is accusative singular.

Why?

• The preposition in takes the accusative when it shows motion toward a place.
• The verb festinamus suggests movement.
• So oppidum must be accusative.

Also, oppidum is a second-declension neuter noun, so its nominative singular and accusative singular both look the same: oppidum.

Festinamus is the first person plural present active indicative of festinare.

Breakdown:

• festinare = to hurry
• festinamus = we hurry / we are hurrying

The -mus ending tells you the subject is we.

So:

• et nos in oppidum festinamus = and we hurry into the town

Yes. Et is the ordinary Latin word for and.

It links the two parts of the sentence:

• Iter longum est
• et nos in oppidum festinamus

So the whole sentence means:

• The journey is long, and we are hurrying into the town.

Nothing unusual is happening with et here.

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

So this sentence could be rearranged in several ways without changing the basic meaning, for example:

• Longum iter est, et nos in oppidum festinamus.
• Et nos in oppidum festinamus; iter longum est.
• In oppidum nos festinamus, et iter longum est.

However, word order can affect emphasis.

For example:

• Longum iter est emphasizes long
• Nos near the front can emphasize we
• In oppidum near the front can emphasize the destination

So the order is flexible, but not meaningless.

Yes, absolutely.

Latin often leaves out subject pronouns because the verb ending already tells you the subject.

So both of these are correct:

• et nos in oppidum festinamus
• et in oppidum festinamus

The second is more neutral and probably more common unless the speaker wants emphasis on we.

Both can express movement toward a place, but they are not exactly the same.

• in oppidum usually suggests movement into the town
• ad oppidum usually suggests movement to the town, toward it, or up to it

So:

• in oppidum festinamus = we hurry into the town
• ad oppidum festinamus = we hurry to/toward the town

In this sentence, in oppidum suggests actual entry into the town.

That is a very good observation. Iter is a third-declension neuter noun.

Its principal forms are:

• iter = nominative singular
• itineris = genitive singular

So it behaves like other neuter third-declension nouns, even though its nominative singular form may look unusual at first.

Some forms are:

• nominative singular: iter
• accusative singular: iter
• genitive singular: itineris

That is why you should memorize it as iter, itineris, n.

It is being used as a predicate adjective.

That means it describes the subject through a form of to be:

• iter = subject
• est = is
• longum = predicate adjective

So this is not a long journey in the sense of an adjective directly attached inside a noun phrase. Instead, it is:

• the journey is long

Latin uses adjectives this way very often.