Avus tibi fabulam de familia sua narrat.

Because avus is the subject of the sentence, so it is in the nominative singular.

• avus = grandfather
• nominative singular is the form used for who is doing the action

Here, the grandfather is the one doing the telling.

Tibi is the dative singular form of tu.

It means to you or for you, not just you.

Latin often uses:

• dative for the indirect object
• accusative for the direct object

So in this sentence:

• tibi = to you
• fabulam = the thing being told

If Latin used te, that would be accusative, and it would suggest you were the direct object, which is not the meaning here.

Because fabulam is in the accusative singular.

It is the direct object of narrat:

• the grandfather tells a story
• the story is what is being told

So:

• nominative: fabula
• accusative: fabulam

This is a very common pattern for first-declension nouns.

Yes, but they are different kinds of objects.

• fabulam is the direct object: the thing told
• tibi is the indirect object: the person to whom it is told

English does this too:

• Grandfather tells you a story

Here:

• you = indirect object
• a story = direct object

Latin marks that difference with cases much more clearly than English does.

Because de is a preposition that takes the ablative case.

So after de, familia must be in the ablative:

• nominative: familia
• ablative: familiā

In many texts without macrons, familiā is simply written familia, so the form looks the same.

So:

• de familia sua = about his own family

If you had familiam suam, that would be accusative, and it would not fit after de.

Here de means about or concerning.

So:

• fabulam de familia sua = a story about his own family

Depending on context, de can also mean things like from, down from, or concerning, but here about is the natural meaning.

Because sua is a reflexive possessive adjective. It refers back to the subject of the sentence.

The subject here is avus, so:

• familia sua = his own family = the grandfather’s own family

Latin uses:

• suus, sua, suum when the owner is the subject
• eius when the owner is someone else

So:

• de familia sua = about his own family
• de familia eius would mean about his/her family, referring to some other person, not the subject

Because sua agrees with familia in gender, number, and case.

• familia is feminine singular
• after de, it is ablative singular
• so the adjective must also be feminine singular ablative: suā
• without macrons, that is written sua

In Latin, adjectives match the nouns they describe, even if English does not show that as clearly.

Narrat is:

• third person singular
• present tense
• active voice
• indicative mood

It comes from the verb narrare, meaning to tell or to relate.

So narrat means:

• he tells
• she tells
• it tells

Here, because the subject is avus, it means he tells.

Latin word order is much more flexible than English word order because Latin uses case endings to show each word’s role.

A very common Latin pattern is:

• subject + other elements + verb

So putting narrat at the end is normal and natural.

But Latin could rearrange the sentence for emphasis, for example:

• Avus fabulam tibi de familia sua narrat
• Tibi avus fabulam de familia sua narrat

The basic meaning would stay the same, because the case endings still show what each word is doing.

Because Latin does not have articles like English the or a/an.

So avus can mean:

• a grandfather
• the grandfather

And fabulam can mean:

• a story
• the story

You decide from the context which English article makes the most sense.

Because Latin often packs grammatical information into word endings.

For example:

• tibi already shows to you through the dative ending
• fabulam already shows that it is the direct object through the accusative ending

Latin still uses prepositions when needed, such as de, but overall it relies much more on endings than English does.