Serva saccum gravem in vestibulo deponit.

Serva is the subject of the sentence, and it is in the nominative singular form.

It comes from the noun serva, meaning female slave or maidservant. In the first declension, the nominative singular often ends in -a.

So here:

• serva = the maidservant / female slave as the one doing the action

Saccum is the direct object of deponit, so it is in the accusative singular.

The noun is saccus = bag, sack.
Its accusative singular form is saccum.

So:

• saccus = a sack, as a dictionary form
• saccum = the sack, as the thing being put down

A very common pattern in Latin is:

• subject in the nominative
• direct object in the accusative

Because gravem is an adjective agreeing with saccum.

The adjective is gravis, meaning heavy. But Latin adjectives change form to match the noun they describe in:

• gender
• number
• case

Since saccum is:

• masculine
• singular
• accusative

the adjective must also be:

• masculine
• singular
• accusative

So:

• saccus gravis = a heavy sack if both were nominative
• saccum gravem = a heavy sack as the direct object

Because in with the ablative usually means in or on in the sense of location.

Here the meaning is in the entrance hall / in the vestibule, so Latin uses:

• in + ablative for where something happens

Thus:

• vestibulum = nominative/accusative form of the noun
• vestibulo = ablative singular after in

A very important contrast is:

• in vestibulo = in the vestibule / inside the vestibule (location)
• in vestibulum = into the vestibule (motion toward)

Deponit is a third person singular present active indicative form of deponere.

That means:

• third person singular = he/she/it
• present = is putting down / puts down
• active = the subject performs the action
• indicative = a normal statement

So deponit means:

• she puts down
• she is putting down

Because the subject is serva, the natural translation is the maidservant puts down or is putting down.

You know because of both case and verb agreement.

• serva is nominative, which is the normal case for the subject
• deponit is third person singular, so it needs a singular subject
• saccum is accusative, so it is functioning as the direct object, not the subject

So the structure is:

• serva = subject
• saccum gravem = direct object
• in vestibulo = prepositional phrase
• deponit = verb

Latin word order is much freer than English word order because the endings show the grammatical roles.

A very common Latin pattern is:

• subject ... object ... verb

So Serva saccum gravem in vestibulo deponit is perfectly natural.

In English, we usually need a stricter order:

• The maidservant puts down the heavy sack in the vestibule

Latin can move words around for emphasis more easily, for example:

• Saccum gravem serva in vestibulo deponit
• In vestibulo serva saccum gravem deponit

These all mean roughly the same basic thing, though the emphasis may shift.

No. Classical Latin does not have articles like English the and a/an.

So serva can mean:

• a maidservant
• the maidservant

And saccum gravem can mean:

• a heavy sack
• the heavy sack

Which one sounds best depends on the context and the translation you are given.

Yes. The verb deponere has a basic sense of put down, set down, or lay aside.

Depending on context, it can be translated in several natural English ways, such as:

• puts down
• sets down
• lays down
• deposits

In this sentence, puts down or sets down is probably the most natural translation.

Yes. Serva is a feminine noun. It is the feminine counterpart of servus.

So:

• servus = male slave / male servant
• serva = female slave / maidservant

That is why the sentence is understood as she puts down rather than he puts down.

Yes, it could come before. Latin adjectives can often appear either before or after the noun.

So both of these are possible:

• saccum gravem
• gravem saccum

Both mean heavy sack.

In many simple sentences, adjective placement is fairly flexible, though sometimes authors use word order for emphasis or style. For a learner, the main thing is not the position but the agreement:

• saccum and gravem match in case, number, and gender

Yes. The Latin present tense often covers both ideas.

So deponit can be translated as:

• puts down = simple present
• is putting down = present progressive

English chooses between those forms more sharply than Latin often does. The context usually tells you which sounds better.