Learn Hardcore Indonesian: Setiap langkah kecil penting bagi kesehatan. - Every small step is important for health.

So "Setiap langkah kecil penting" literally feels like "Every small step important", which in natural English becomes "Every small step is important."

You only use adalah (often translated as "is") mainly before nouns, not before adjectives:

Dia adalah dokter. = He/She is a doctor.
But:
Dia pintar. (no adalah) = He/She is smart.

What exactly does setiap mean, and how is it different from tiap?

Setiap means "every" or "each".

Setiap langkah kecil = every/each small step.

Tiap is just a shorter, slightly more informal version of setiap. In this sentence you could also say:

Tiap langkah kecil penting bagi kesehatan.

Both are correct; setiap is a bit more neutral/formal, tiap feels a bit more casual, but the meaning is basically the same.

Why is it langkah kecil and not kecil langkah?

In Indonesian, adjectives usually come after the noun they describe.

langkah kecil = small step (literally: step small)
rumah besar = big house
baju merah = red shirt

So:

langkah kecil ✅ (correct)
kecil langkah ❌ (incorrect / unnatural)

The order in the sentence is:

setiap (every) + langkah (noun: step) + kecil (adjective: small)

Does langkah here mean one single step, or many steps?

Grammatically, langkah is singular, but Indonesian often does not mark plural with an ending like -s.

Setiap langkah kecil is understood as:

"each small step" (focusing on each one individually) and in total it refers to many steps.

If you really needed to emphasize plurality, you might see:

langkah-langkah kecil = (many) small steps

But in this sentence, setiap langkah kecil is natural and already implies a series of individual steps.

What does penting do in this sentence?

Penting is an adjective meaning "important".

In this sentence, it functions as the main predicate (like an adjective acting as a verb in English "to be important"):

Setiap langkah kecil (subject)
penting (predicate: is important)
bagi kesehatan (prepositional phrase: for health)

So the structure is: Subject + Adjective + Prepositional phrase.

What is the function of bagi here? Could I use untuk instead?

Bagi is a preposition often translated as "for" (in the sense of beneficial / relevant to something, often abstract):

penting bagi kesehatan = important for health

You can also say:

penting untuk kesehatan

Differences:

bagi tends to sound a bit more formal and is very common in written or neutral style.
untuk is very common and neutral, used in many situations.
buat is more colloquial, especially in spoken Indonesian:
penting buat kesehatan (informal).

All three are understandable; for standard usage, bagi or untuk are safest.

What is the difference between sehat and kesehatan?

sehat = healthy (adjective)
- Dia sehat. = He/She is healthy.
kesehatan = health (noun)

Kesehatan is formed from:

root: sehat
prefix ke-
- suffix -an → kesehatan (the state/condition of being healthy)

So:

penting bagi kesehatan = important for health
You cannot use sehat there; it must be the noun form.

Could I put bagi kesehatan somewhere else in the sentence?

The most natural position is exactly as given:

Setiap langkah kecil penting bagi kesehatan.

You could move it to the front for emphasis in some contexts:

Bagi kesehatan, setiap langkah kecil penting.

This sounds a bit more formal or rhetorical, like in a speech or article title. In everyday sentences, keeping bagi kesehatan after penting is the most common and natural order.

Can I add itu or ini, like Setiap langkah kecil itu penting bagi kesehatan? What changes?

Yes, you can say:

Setiap langkah kecil itu penting bagi kesehatan.

Adding itu gives a sense of specific reference or emphasis, similar to:

"Those small steps"
or "Those every little steps (we talked about)" are important for health.

Nuance:

Without itu: general statement, a generic truth.
Setiap langkah kecil penting bagi kesehatan.
With itu: refers to steps already mentioned, seen, or contextually known.
Setiap langkah kecil itu penting bagi kesehatan.

How do I express past or future with this sentence? There is no tense marker.

Indonesian verbs and adjectives do not change form for tense. Time is usually shown by time words or understood from context.

Base sentence (timeless/general truth):

Setiap langkah kecil penting bagi kesehatan.
= Every small step is important for health.

To make the time explicit:

Past:
Dulu, setiap langkah kecil penting bagi kesehatan saya.
(In the past, every small step was important for my health.)
Future:
Ke depan, setiap langkah kecil akan penting bagi kesehatanmu.
(In the future, every small step will be important for your health.)

Often, for a general statement like this, Indonesians just leave it tenseless, as in the original sentence.