Prodavnica je u mojoj ulici.

Because after the preposition u when it means in / at / on, Serbian normally uses the locative case.

So:

• moja ulica = my street (dictionary/basic form)
• u mojoj ulici = in/on my street (locative)

Both words change:

• moja → mojoj
• ulica → ulici

This is very common in Serbian: the adjective and noun usually both change to match the case.

It is the locative singular.

Here is the breakdown:

• ulica is a feminine noun
• in the locative singular, ulica becomes ulici
• the possessive adjective moja also has to match, so it becomes mojoj

So u mojoj ulici is a feminine singular locative phrase.

Because moja has to agree with ulica in:

• gender: feminine
• number: singular
• case: locative

The basic form is:

• moja ulica = my street

But after u, you need the locative:

• u mojoj ulici

This kind of agreement is a core feature of Serbian grammar.

Because ulica is in the locative singular after u.

Many feminine nouns ending in -a change like this:

• nominative: ulica
• locative: ulici

Other examples of the same pattern:

• škola → u školi
• soba → u sobi
• kuća → u kući

So ulica → ulici fits a very common pattern.

Here u means in, at, or idiomatically in English often on.

So u mojoj ulici literally looks like in my street, but natural English often says on my street.

In Serbian, u is the normal preposition here. Serbian does not have to match English prepositions word-for-word.

Je is the 3rd person singular form of the verb biti (to be) in the present tense.

So:

• Prodavnica = the store / shop
• je = is
• u mojoj ulici = on/in my street

Together: The store is on my street.

Unlike in some languages where the verb to be can be omitted in the present tense, in Serbian it is normally expressed here.

Yes. Prodavnica is a feminine noun.

You can tell partly because it ends in -a, which is a very common feminine ending in Serbian.

That matters because adjectives and some other words must agree with nouns in gender. In this sentence, though, the possessive mojoj agrees with ulici, not with prodavnica, because it belongs to the phrase my street.

Yes. Serbian word order is more flexible than English word order.

The neutral order here is:

• Prodavnica je u mojoj ulici.

But you could also hear:

• U mojoj ulici je prodavnica.

That version puts more focus on in my street.

Even when word order changes, the case endings still show the grammatical relationships, so the meaning remains clear.

It can mean either store or shop, depending on context.

A few rough equivalents are:

• prodavnica = store / shop
• radnja can also mean shop, though usage depends on region and context

For a learner, prodavnica is a very common and useful everyday word.

A rough pronunciation is MO-yoy.

More precisely:

• mo sounds like mo in more, but shorter
• j in Serbian is pronounced like English y
• so mojoj sounds approximately like MO-yoy

Also:

• ulici is roughly OO-lee-tsee
• prodavnica is roughly pro-DAHV-nee-tsa

These are only approximations, but they are a good start for an English speaker.

Usually, for this meaning, u mojoj ulici is the normal and expected choice.

English says on my street, but Serbian commonly uses u here, not na.

This is one of those cases where it is better not to translate the preposition directly from English. The natural Serbian expression is:

• Prodavnica je u mojoj ulici.

No. Serbian does not have articles like a or the.

So prodavnica can mean:

• a store
• the store

The exact meaning depends on context.

In this sentence, English will often translate it as The store is on my street or There is a store on my street, depending on the situation.