U zdjelici je salata od krumpira.

Because u meaning in takes the locative case when it refers to location.

• base form: zdjelica = bowl
• locative singular: zdjelici
• so: u zdjelici = in the bowl

In Croatian, you usually cannot leave the noun in its dictionary form after a preposition like u when you are talking about location.

It is locative singular.

The preposition u can take:

• locative for being in a place
• accusative for movement into a place

So here:

• u zdjelici = in the bowl → location → locative

Compare:

• Salata je u zdjelici. = The salad is in the bowl.
• Stavljam salatu u zdjelicu. = I am putting the salad into the bowl.

Je is the 3rd person singular present of the verb biti = to be.

So here it means is.

• U zdjelici je salata od krumpira.
• literally: In the bowl is potato salad.

Croatian does not need a separate word like English there in there is. The idea of there is is often expressed simply with je plus normal sentence structure.

Because Croatian does not use a dummy subject like English there.

English says:

• There is potato salad in the bowl.

Croatian usually just says:

• U zdjelici je salata od krumpira.

So Croatian expresses the same idea without adding a meaningless filler word. The sentence is built more directly.

Yes. Salata is the grammatical subject, and it is in the nominative singular.

You can tell because:

• salata is in its basic form
• the verb je is singular, matching salata

So structurally:

• U zdjelici = location
• je = is
• salata od krumpira = potato salad

Yes, both are possible.

Croatian word order is more flexible than English, and changing the order often changes the focus.

• U zdjelici je salata od krumpira.
  Focuses more on where it is or introduces what is in the bowl.
• Salata od krumpira je u zdjelici.
  Focuses more on the potato salad itself.

Both are grammatical. The version with U zdjelici first sounds very natural when you are describing what is in a certain place.

Because od usually means of, from, or made of, and it requires the genitive case.

Here:

• salata od krumpira = potato salad
• literally: salad of potato

This is a very common Croatian pattern:

• sok od naranče = orange juice
• pire od krumpira = mashed potatoes / potato purée
• juha od rajčice = tomato soup

Because after od, the noun must be in the genitive.

• nominative: krumpir = potato
• genitive singular: krumpira

So:

• od krumpira = of potato / made of potatoes

Even though English just uses potato before salad, Croatian uses the preposition od plus the genitive form.

Because Croatian has no articles.

English distinguishes:

• a bowl
• the bowl

Croatian usually does not. The context tells you whether something is definite or indefinite.

So:

• u zdjelici could mean in a bowl or in the bowl
• salata od krumpira could mean potato salad or the potato salad, depending on context

If needed, Croatian can show definiteness in other ways, but it does not use articles like English.

Yes, that is also possible, but it uses a different noun.

• zdjelica = a small bowl / little bowl
• zdjela = bowl / serving bowl / larger bowl

So:

• u zdjelici = in the small bowl
• u zdjeli = in the bowl

Both are correct Croatian words; the choice depends on what kind of bowl you mean.

A simple pronunciation guide is:

oo ZDYEH-lee-tsee yeh sah-LAH-tah od KROOM-pee-rah

A few useful notes:

• u sounds like oo in food
• j is like English y in yes
• lj is a soft sound, roughly like lli in million for many learners
• c is pronounced ts

So:

• zdjelici ends roughly like -lee-tsee
• je sounds like yeh

Yes, it is a natural and correct sentence.

A few natural alternatives are also possible, depending on emphasis:

• Salata od krumpira je u zdjelici.
• U zdjeli je salata od krumpira.
• U zdjelici ima salate od krumpira.

That last one, with ima, is slightly different in feel:

• U zdjelici je salata od krumpira. = There is potato salad in the bowl / The potato salad is in the bowl.
• U zdjelici ima salate od krumpira. = There is some potato salad in the bowl.

So the original sentence is absolutely normal and idiomatic.