Njemu se sviđa ova ideja.

Because on means he in the nominative case, but this sentence needs the dative case: njemu = to him.

The verb pattern is sviđati se + dative. So Croatian structures this idea more like:

This idea is pleasing to him

rather than:

He likes this idea

So in this sentence:

• ova ideja is the grammatical subject
• njemu is the person affected by it

Njemu is dative singular.

It is dative because sviđati se takes:

• the person in the dative
• the thing liked in the nominative

That is one of the most important things to remember with this verb.

Here, se is part of the verb expression sviđati se. It does not mean himself or itself in this sentence.

So you should learn sviđati se as a unit:

• sviđati se = to be appealing / to be pleasing

You normally cannot just remove se and keep the same meaning.

Because the subject is ova ideja, which is singular.

The verb agrees with the subject, not with njemu. Since ideja is singular, the verb is singular too:

• ova ideja se sviđa → singular
• ove ideje se sviđaju → plural

So sviđa is the correct 3rd person singular present form.

Because ova ideja is in the nominative, and it is the subject of the sentence.

With sviđati se, the thing that is liked is not a direct object. That is why it stays in the nominative:

• ova ideja = nominative
• ovu ideju = accusative

English speakers often expect the accusative here because English uses a direct object in He likes this idea, but Croatian does not.

Because ideja is a feminine singular noun, and the demonstrative must agree with it.

So:

• ovaj = masculine singular
• ovo = neuter singular
• ova = feminine singular

Since ideja is feminine, you need ova.

Yes. Mu is the short, unstressed form of njemu.

So these are both possible:

• Njemu se sviđa ova ideja.
• Ova ideja mu se sviđa.
• Sviđa mu se ova ideja.

The difference is mostly about emphasis:

• mu is the normal, neutral clitic form
• njemu is fuller and often sounds more emphatic or contrastive

For example, Njemu se sviđa ova ideja, ali meni ne puts extra focus on him.

No, Croatian word order is fairly flexible, but not completely free.

This sentence can appear in different orders depending on what you want to emphasize:

• Njemu se sviđa ova ideja.
• Sviđa mu se ova ideja.
• Ova ideja mu se sviđa.

These all express basically the same core meaning, but the focus changes.

One important detail: short words like mu and se are clitics, so they tend to go in special positions near the beginning of the clause.

It is the normal translation, yes, but the grammar is different.

A more literal English rendering would be:

This idea appeals to him
or
This idea is pleasing to him

That is why Croatian uses:

• dative for the person
• nominative for the thing liked

So the meaning matches English He likes this idea, but the structure does not.

Both can relate to liking, but they are not used in exactly the same way.

• sviđati se often means to appeal to someone, to seem attractive, to be pleasing
• voljeti often means to love or to like in a stronger, broader sense

For an idea, design, plan, song, or appearance, sviđati se is very common and natural.

So Njemu se sviđa ova ideja sounds very natural for He likes this idea.

The dictionary form is sviđati se.

In this sentence, sviđa is the present-tense singular form.

A useful pair to know is:

• sviđati se = imperfective
• svidjeti se = perfective

For example:

• Sviđa mu se ova ideja. = He likes this idea / This idea appeals to him.
• Svidjela mu se ova ideja. = He came to like this idea / This idea appealed to him.

That aspect difference becomes important later, but it is good to notice it early.