Ako ti se ovaj kolač ne sviđa, uzmi drugi.

Croatian often expresses liking with the verb sviđati se, which works differently from English.

• sviđati se literally behaves like to be pleasing to
• So Ovaj kolač ti se sviđa is structurally closer to This cake is pleasing to you
• ti = to you
• se is a fixed part of the verb
• sviđa = the verb form

By contrast, voljeti means to love or to like in a stronger, more direct way, and it takes a direct object:

• Voliš ovaj kolač = You like/love this cake

So in this sentence, sviđati se is the natural choice for if you don’t like this cake...

ti is the dative singular form of ti/you.

With sviđati se, the person who experiences the liking goes in the dative:

• Meni se sviđa = I like it / It pleases me
• Tebi se sviđa = You like it / It pleases you
• Ti se sviđa is the short unstressed form of tebi se sviđa

So Ako ti se ovaj kolač ne sviđa... literally means:

• If this cake is not pleasing to you...

se is part of the verb sviđati se. You generally learn this verb together with se, because it normally appears that way.

So:

• sviđati se = to be pleasing / to be liked
• sviđa mi se = I like it
• ne sviđa mi se = I don’t like it

Even though se often appears with reflexive verbs, here you should mainly think of sviđati se as a set expression.

Croatian word order is more flexible than English, but clitics like ti and se usually come very early in the clause, often in the second position.

That is why you get:

• Ako ti se ovaj kolač ne sviđa...

rather than something more English-like such as:

• Ako ovaj kolač ti se ne sviđa...

The short words ti and se are unstressed clitics, and they tend to cluster near the beginning of the clause.

ovaj means this, and it must agree with the noun it describes.

kolač is:

• masculine
• singular
• nominative here, because it is the subject of sviđa

So the correct form is:

• ovaj kolač = this cake

If the noun changed, the form of ovaj would change too.

Because with sviđati se, the thing being liked is the grammatical subject.

In English, we say:

• You like this cake

But Croatian structures it more like:

• This cake pleases you

So:

• ovaj kolač is the subject
• therefore it is in the nominative

That is why you do not get an accusative form here.

Croatian usually forms negation by placing ne before the verb.

So:

• sviđa se = is pleasing / is liked
• ne sviđa se = is not pleasing / is not liked

In this sentence:

• Ako ti se ovaj kolač ne sviđa = If you don’t like this cake

Notice that ne goes directly with the verb form sviđa.

uzmi is the imperative singular of uzeti (to take).

It is used when speaking directly to one person:

• uzmi = take
• uzmite = take (plural or polite singular)

So:

• uzmi drugi = take another one

This matches the sentence because the speaker is telling one person what to do if they do not like the cake.

Croatian often omits a noun when it is obvious from context.

Here, drugi means:

• another one
• literally the second/other one

Because kolač was already mentioned, you do not need to repeat it:

• uzmi drugi = take another one
• understood: another cake

If you wanted, you could also say uzmi drugi kolač, but it is less economical and not necessary here.

drugi agrees with the implied noun kolač.

Since kolač is:

• masculine
• singular

the adjective/pronominal form is also:

• drugi

It stands in the case required by the verb uzmi. Since uzeti takes a direct object, the object is in the accusative. For masculine inanimate nouns, accusative singular looks like nominative singular, so drugi stays drugi.

That is why:

• uzmi drugi is correct

Yes. That would be the plural or polite version.

Compare:

• ti ... uzmi = speaking to one person informally
• vam ... uzmite = speaking to several people, or to one person formally/politely

So your original sentence is informal singular.

Because Ako ti se ovaj kolač ne sviđa is a subordinate conditional clause introduced by ako (if), and it is followed by the main clause:

• uzmi drugi

Croatian normally separates these with a comma:

• Ako ti se ovaj kolač ne sviđa, uzmi drugi.

So the comma works much like in English with an initial if clause.