Si apis puerum pungit, mater statim aquam frigidam affert.

Because apis is the subject of the verb pungit. In Latin, the subject of a verb goes in the nominative case.

So here:

• apis = the bee as the one doing the stinging
• pungit = stings

Apis is a third-declension noun, and its nominative singular happens to be the same as its dictionary form.

Because puerum is the direct object of pungit. It is the person receiving the action.

• apis stings puerum
• so puerum must be in the accusative case

The noun puer, pueri is a second-declension masculine noun:

• nominative singular: puer = boy as subject
• accusative singular: puerum = boy as object

So Latin uses the ending -um to show that the boy is being stung, not doing the stinging.

Because mater is the subject of the second verb, affert.

In the second clause:

• mater = the mother
• affert = brings

Since she is doing the action, mater must be in the nominative case.

If she were the direct object, then you would expect matrem instead.

Because aquam frigidam means cold water, and both words must agree.

• aquam is the noun, in the accusative singular
• frigidam is the adjective modifying it, also in the accusative singular

In Latin, adjectives must agree with the nouns they describe in:

• gender
• number
• case

So because aqua is feminine singular accusative here, the adjective must also be feminine singular accusative:

• aqua frigida = cold water as subject
• aquam frigidam = cold water as object

Yes, it could come before it.

Latin word order is much more flexible than English word order because the endings show the grammatical job of each word. So both of these are possible:

• aquam frigidam
• frigidam aquam

Both mean the same thing: cold water.

The choice often depends on style, emphasis, or the rhythm of the sentence.

Si means if and introduces a conditional clause.

So the sentence has two parts:

• Si apis puerum pungit = If a bee stings the boy
• mater statim aquam frigidam affert = the mother immediately brings cold water

Si does not change the case of a noun. It simply introduces the condition.

Latin often uses the present indicative for a simple or general condition, just as English can.

So this sentence means something like:

• If a bee stings the boy, the mother immediately brings cold water
• or more naturally in English, If a bee stings the boy, his mother immediately brings cold water

This is a straightforward, real condition, not a hypothetical or contrary-to-fact one.

Because Latin has no articles.

English distinguishes between:

• a bee
• the bee

Latin usually does not. A noun like apis can mean:

• a bee
• the bee

The exact meaning depends on context.

The same is true for:

• puerum = a boy or the boy
• mater = a mother or the mother

Statim is an adverb, meaning immediately or at once.

It modifies the verb affert:

• mater statim aquam frigidam affert
• the mother immediately brings cold water

Its position is fairly flexible. Latin often places adverbs where they sound natural or where the writer wants emphasis. So statim does not have to stand in exactly the same place it would in English.

Because affert is the verb afferre, which means to bring to or simply to bring.

It is a compound of:

• ad- = to, toward
• ferre = to carry, bear

So:

• fert = carries
• affert = brings

In this sentence, affert is the natural choice because the mother is bringing the water to the boy.

In Latin, the endings are more important than the word order.

Here is how you can tell:

• apis is nominative, so it is the subject of pungit
• puerum is accusative, so it is the object of pungit
• mater is nominative, so it is the subject of affert
• aquam frigidam is accusative, so it is the object of affert

That means Latin can move words around more freely without losing the basic meaning.

For example, these still make sense grammatically:

• Si puerum apis pungit, mater statim aquam frigidam affert
• Si apis puerum pungit, aquam frigidam mater statim affert

The emphasis changes, but the case endings still show the grammatical roles.

Yes, apis is normally feminine.

That matters especially when an adjective refers to it. In this sentence there is no adjective describing apis, so you do not see the gender affecting anything directly. But it is still useful to know for later sentences.

For example:

• apis parva = the small bee

Here parva is feminine because apis is feminine.

A learner often wants to identify the base form of each word. Here they are:

Nouns:

• apis, apis = bee
• puer, pueri = boy
• mater, matris = mother
• aqua, aquae = water

Verbs:

• pungo, pungere = sting, prick
• affero, afferre = bring

From those dictionary forms, the sentence uses these forms:

• apis = nominative singular
• puerum = accusative singular
• mater = nominative singular
• aquam = accusative singular
• pungit = third person singular present
• affert = third person singular present

Yes, very naturally.

Latin often leaves possession unstated when it is obvious from context. So mater here can simply mean:

• the mother
• or, in more natural English, his mother

Latin does have possessive words such as eius or suus, but it does not always need them when the relationship is clear.

So a natural English translation could be:

• If a bee stings the boy, his mother immediately brings cold water.