Susjeda mi ju je dala jučer; u toj staklenci je stvarno dobar džem.

Susjeda means female neighbor.
The masculine form is susjed.

So here the subject is specifically a woman:

• susjed = a male neighbor
• susjeda = a female neighbor

Because the subject is feminine, that also affects the past-tense form later in the sentence: dala.

Croatian past tense is built with:

• the auxiliary je
• a past participle that agrees with the subject in gender and number

Here the subject is susjeda (female neighbor), so the participle is feminine singular:

• dao = he gave
• dala = she gave
• dalo = it gave
• dali = they gave (masculine/mixed)
• dale = they gave (all feminine)

So Susjeda mi ju je dala = The female neighbor gave it to me.

Mi is the unstressed dative form of ja (to me).

With dati (to give), Croatian normally works like this:

• giver = nominative
• thing given = accusative
• recipient = dative

So in this sentence:

• susjeda = the giver
• ju = the thing given
• mi = the recipient (to me)

That is why mi means to me here, not my.

Ju is a feminine singular accusative clitic pronoun, meaning her/it depending on context.

In this sentence it most naturally refers to a previously understood feminine noun, very likely staklenka (jar), since the second clause mentions u toj staklenci (in that jar).

So the sense is something like:

• Susjeda mi ju je dala jučer = My female neighbor gave it/the jar to me yesterday

Croatian often uses a pronoun instead of repeating the noun when the referent is already clear.

For feminine singular accusative, Croatian can use ju or je in some contexts.

But here ju is used because the sentence already contains the auxiliary je:

• mi ju je dala

If you used je as the pronoun too, you would get mi je je dala, which is awkward and confusing.

So ju is the normal choice here to keep things clear.

Because these are all clitics: short unstressed words that usually go in second position in the clause.

In Susjeda mi ju je dala jučer, the first stressed word is Susjeda, and then the clitic cluster follows:

• mi = to me
• ju = it/her
• je = auxiliary

This kind of ordering is very typical in Croatian and often does not match English word order.

So although English says The neighbor gave it to me yesterday, Croatian naturally says something closer to:

• Neighbor to-me it has given yesterday

but with normal Croatian clitic placement:

• Susjeda mi ju je dala jučer

Yes. Jučer (yesterday) is fairly mobile.

For example, these are all possible:

• Susjeda mi ju je dala jučer.
• Jučer mi ju je susjeda dala.
• Susjeda mi ju je jučer dala.

They all mean roughly the same thing, but the emphasis changes slightly.

A useful thing to remember: even when words move around, the clitics still usually stay together near the beginning of the clause.

Because u can take different cases depending on meaning:

• u + accusative = motion into
• u + locative = location in

Here the meaning is location: in that jar, so Croatian uses the locative.

The noun is:

• staklenka = jar

Its locative singular is:

• staklenci

And the demonstrative ta (that) must match it:

• toj staklenci = in that jar

Compare:

• u tu staklenku = into that jar
• u toj staklenci = in that jar

Because toj is the feminine singular locative/dative form of ta (that).

It has to agree with staklenci, which is:

• feminine
• singular
• locative

So:

• ta staklenka = that jar
• u toj staklenci = in that jar

This is just normal adjective/demonstrative agreement in Croatian.

Because after je in this sentence, džem is the subject/predicate expression in the nominative.

• džem is masculine singular
• dobar agrees with it in masculine singular nominative

So:

• dobar džem = good jam

Croatian often uses this structure where English might say there is:

• U toj staklenci je stvarno dobar džem.
• literally: In that jar is really good jam.

So džem stays nominative here.

Stvarno means really.

It is an adverb modifying dobar:

• stvarno dobar džem = really good jam

So the second clause means:

• There is really good jam in that jar or more literally
• In that jar is really good jam

The semicolon links two closely related independent clauses:

• Susjeda mi ju je dala jučer
• u toj staklenci je stvarno dobar džem

The second clause explains or comments on the first, so a semicolon works well stylistically.

A full stop would also be possible:

• Susjeda mi ju je dala jučer. U toj staklenci je stvarno dobar džem.

A comma would usually be less standard here because these are two complete clauses.

Yes — mainly these three things:

1. Croatian uses clitics heavily
   Words like mi, ju, and je are short unstressed forms that follow special placement rules.

2. Word order is more flexible than in English
   Croatian often moves words for emphasis, while still keeping clitics in their usual position.

3. Cases carry a lot of meaning
   You understand who gave what to whom partly from the case forms:

   • susjeda = subject
   • mi = recipient
   • ju = direct object
   • u toj staklenci = location

So even though the sentence may look unusual from an English perspective, it is built in a very normal Croatian way.