Learn Hardcore Croatian: Kada se dobro koncentriram, lakše držim pažnju i svakodnevno učim bez stresa. - When I concentrate well, it is easier to keep my attention and I study every day without stress.

koncentrirati se = to concentrate (to focus your mind)
Without se, koncentrirati is rare in everyday speech and sounds incomplete/wrong in this meaning.

So kada se dobro koncentriram literally is “when I concentrate well (myself).”
Leaving out se here would sound ungrammatical to native speakers.

What exactly does se mean here? Is it like “myself”?

Se is a reflexive clitic pronoun, but in many Croatian reflexive verbs it doesn’t translate directly as a separate word.

In koncentriram se, you could think of it as “I concentrate myself,” but in English we just say “I concentrate.”
So often you don’t translate se at all; you just know that the verb is reflexive in Croatian.

The important thing is: you must use se with verbs that are reflexive in Croatian, even if English doesn’t show it with “myself/yourself/etc.”

Why is the word order kada se dobro koncentriram and not kada dobro se koncentriram?

In Croatian, se is a clitic (a short, unstressed word) and clitics usually go in second position in the clause.

The first “position” is usually the first full word (here kada).
Then come clitics: kada se dobro koncentriram.
Dobro is not a clitic, so it comes after se.

Forms like kada dobro se koncentriram sound wrong because se is not in its preferred second position.

Can I say dobro se koncentriram without kada?

Yes.

Dobro se koncentriram. = “I concentrate well.”

Here, dobro is the first full word in the sentence, so se again takes the second position: dobro se.
You still cannot say dobro koncentriram se; the clitic se should not be pushed to the end.

Why is there a comma after kada se dobro koncentriram?

Croatian usually uses a comma between a dependent clause and the main clause.

Kada se dobro koncentriram, = “When I concentrate well,” → dependent clause
lakše držim pažnju i svakodnevno učim bez stresa. = main clause

So we write:
Kada se dobro koncentriram, lakše držim pažnju i svakodnevno učim bez stresa.

What is lakše, and why is there no word like “više” or “više lako”?

Lakše is the comparative form of the adverb lako (“easily”).

lako = easily
lakše = more easily

In English you add “more”; in Croatian you usually change the word form instead:

lako učim = I learn easily
lakše učim = I learn more easily

You do not say više lako in this meaning; you use lakše.

Why is it pažnju and not pažnja in držim pažnju?

Pažnja is a feminine noun.

Nominative (dictionary form): pažnja = attention
Accusative (direct object): pažnju

In držim pažnju (“I hold/keep attention”), pažnju is the direct object, so it must be in the accusative case.
That’s why it changes to -u: pažnja → pažnju.

Is držim pažnju a common way to say “I stay focused”? Could I say something else?

Yes, držim pažnju is natural and understandable. It literally means “I hold/keep (my) attention.”

Other common options:

održavam pažnju – I maintain attention
ostajem koncentriran / ostajem koncentrirana – I stay concentrated/focused
lakše pratim – I follow (what’s going on) more easily

In your sentence, lakše držim pažnju sounds very natural.

What’s the difference between svakodnevno učim and učim svaki dan?

They mean almost the same thing:

svakodnevno učim = I study/learn daily, I learn on a daily basis
(adverb svakodnevno = “everyday, daily”)
učim svaki dan = I study every day
(phrase svaki dan = “every day”)

Svakodnevno učim sounds a bit more compact/formal; učim svaki dan sounds slightly more conversational, but both are very common.

Why is it bez stresa and not bez stres?

The preposition bez (“without”) always takes the genitive case.

Nominative: stres
Genitive: stresa

So you must say bez stresa = “without stress.”
Using the nominative (bez stres) would be ungrammatical.

Could I add ja at the beginning: Ja se dobro koncentriram…? Is it wrong to leave it out?

You can add ja, but it changes the nuance:

Se dobro koncentriram is impossible – you need something before se.
Ja se dobro koncentriram, lakše držim pažnju…
This is correct and often sounds like emphasis: “I (as opposed to someone else) concentrate well…”

In normal, neutral statements, Croatian usually drops the subject pronoun because the verb ending (-am, -im, etc.) already shows the person.
So Kada se dobro koncentriram… is the most natural neutral version.

What’s the difference between učim and naučim here? Why is it učim?

Učim and naučim differ in aspect:

učim (imperfective) = I am learning / I learn (ongoing, habitual process)
naučim (perfective) = I learn something completely, I manage to learn it, I end up knowing it

In your sentence:

svakodnevno učim bez stresa = “I study/learn every day without stress” → describes an ongoing, repeated activity, so the imperfective učim is correct.
svakodnevno naučim would sound like “every day I manage to (completely) learn (something),” which is a different focus.

Why do we have koncentriram (with -am) but učim (with -im) if both mean “I …” in the present tense?

Croatian verbs belong to different conjugation types, which use different present tense endings:

koncentrirati se → koncentriram (se)
– infinitive in -irati → 1st person sg. ends in -am
(koncentriram, koncentriraš, koncentrira, …)
učiti → učim
– infinitive in -iti → 1st person sg. often ends in -im
(učim, učiš, uči, …)

So both are 1st person singular present, just from different verb groups.