S jedne strane trema, s druge strane komunikacijske vještine.

It is a very common Croatian pattern meaning on the one hand ... on the other hand ....

So:

• S jedne strane trema = On the one hand, nervousness / stage fright
• s druge strane komunikacijske vještine = on the other hand, communication skills

It sets up a contrast between two things.

Because Croatian often allows elliptical sentences, especially in speech, notes, headlines, presentations, or short written comments.

The full version could be something like:

• S jedne strane je trema, a s druge strane su komunikacijske vještine.
• S jedne strane postoji trema, a s druge strane postoje komunikacijske vještine.

But that sounds more explicit and heavier. The shorter version is natural and stylistically neat.

S is the preposition with / from / off, depending on context. In this expression, s jedne strane is an idiomatic phrase that literally feels like from one side and functionally means on one hand / from one perspective.

So this is not a word-for-word English structure, but a fixed Croatian expression:

• s jedne strane = on the one hand
• s druge strane = on the other hand

Because they agree with strane, which is:

• feminine
• singular
• in the genitive

Here is the breakdown:

• strana = side
• jedna strana = one side
• jedne strane = of one side
• druge strane = of the other side

After s in this expression, Croatian uses the genitive, so the adjective changes too:

• jedna → jedne
• druga → druge

In this structure, repeating it is the normal and most natural choice:

• S jedne strane ..., s druge strane ...

This balanced repetition is exactly what makes the contrast clear.

You may hear shortened versions in casual speech, but for learners it is best to treat the full pattern as fixed.

Trema means stage fright, performance anxiety, or nervousness before speaking/performing.

It is not just any kind of fear. It is usually the nervous feeling you get before:

• speaking in public
• giving a presentation
• performing
• being evaluated

So in this sentence, trema suggests nervousness that contrasts with someone’s communication ability.

They are related, but not identical.

• komunikacijske vještine = communication skills
• komunikativne vještine can sound more like communicative abilities or skills related to being communicative

In practice, komunikacijske vještine is the standard and very common phrase for communication skills.

Also:

• vještine = skills
• komunikacijske = communication-related

So this is a straightforward adjective + noun combination.

Because Croatian normally talks about skills in the plural, just like English often does.

• vještina = a skill
• vještine = skills

So komunikacijske vještine means communication skills, not just one single ability.

A comma is enough because the contrast is already strongly signaled by the repeated pattern:

• S jedne strane ... , s druge strane ...

Croatian can also use a:

• S jedne strane trema, a s druge strane komunikacijske vještine.

That version is also correct. The version without a is more compact and slightly more stylistic.

Not in natural English. That would sound odd.

Even though the Croatian literally looks something like from one side / from the other side, the natural English equivalent is:

• On the one hand ... on the other hand ...

So this is a case where you should learn the whole expression as a unit, not translate each word separately.

Normally, the standard form here is s:

• S jedne strane

Croatian uses sa before certain consonants or consonant clusters to make pronunciation easier, for example:

• sa mnom
• sa sestrom

But in this expression, s jedne strane is the normal form.

A little, yes, but the standard pattern is:

• S jedne strane ..., s druge strane ...

That is the most natural order.

You could build a fuller sentence with more variation, for example:

• S jedne strane postoji trema, a s druge strane važne su komunikacijske vještine.

But in the short contrastive phrase you gave, the fixed order is best.

It is basically neutral. The expression s jedne strane ... s druge strane ... works well in:

• everyday speech
• essays
• presentations
• journalism
• formal discussion

So it is very useful and worth memorizing as a standard Croatian contrast structure.