Learn Hardcore Croatian: Subotom ujutro često idem u supermarket po kruh i voće. - On Saturday mornings I often go to the supermarket for bread and fruit.

Subotom idem… = I (usually) go on Saturdays.
U subotu idem… = I (will go) on Saturday (one specific Saturday).
You wouldn’t say just subota idem; the case ending in subotom is what makes it function like an adverb (“on Saturdays”).

Why is Subotom at the beginning of the sentence? Can it move?

Putting Subotom first emphasizes the time frame: “As for Saturdays…”.
You can move it around, for example:

Često subotom ujutro idem u supermarket…
Ujutro subotom često idem u supermarket…
All are grammatically correct; Croatian word order is quite flexible. You usually put at the start what you want to highlight (time, place, frequency, etc.).

What exactly does ujutro mean, and how is it formed?

Ujutro means “in the morning”. Historically it is u + jutro (“in the morning”), fused into one word and now behaves as an adverb.
You normally say:

ujutro – in the morning
poslijepodne – in the afternoon
navečer – in the evening

Why do we say Subotom ujutro and not ujutro subotom? Is there a difference?

Both Subotom ujutro and Ujutro subotom are correct.

Subotom ujutro sounds like you’re first grouping by day (“on Saturdays”) and then specifying time of day (“in the morning”).
Ujutro subotom puts a bit more focus on the morning as the key time.
In everyday speech, they are almost interchangeable; it’s mostly a nuance of emphasis, not grammar.

What does često do here, and where can it go in the sentence?

Često means “often” and is an adverb of frequency. In this sentence it modifies idem (“I go”).
You can place it in several positions:

Često subotom ujutro idem u supermarket…
Subotom ujutro često idem u supermarket… (original)
Idem često subotom ujutro u supermarket…
All are acceptable; putting često earlier tends to stress how often the action happens.

Why is there no word for “the” or “a” in u supermarket?

Croatian does not have articles like “the” or “a/an”.
Whether English would use “a” or “the” is inferred from context in Croatian.
So u supermarket can mean “to the supermarket” or “to a supermarket”, depending on what the speaker has in mind.

Why is it u supermarket, not u supermarketu?

The choice is about motion vs. location:

u + accusative = movement into something
u + locative = being in/at a place
Here we have idem u supermarket (I go to the supermarket), which expresses movement, so supermarket is in the accusative. If you were already there, you’d say u supermarketu sam (“I am in the supermarket”) with the locative ending -u.

What case is supermarket in, and why doesn’t it change form?

Supermarket is masculine, and here it is in the accusative singular after u with a verb of motion (idem u).
For masculine inanimate nouns, the accusative singular looks the same as the nominative singular (no extra ending), so it just stays supermarket.

What does the preposition po mean in po kruh i voće? Why not za kruh i voće?

With motion verbs, po + accusative often means “in order to get / to pick up / to buy” something.

Idem u supermarket po kruh i voće. = I’m going to the supermarket to get/buy bread and fruit.
Za
- accusative can also mean “for”, but idem po kruh is the fixed, natural phrase for going somewhere to pick up bread. Idem za kruh sounds odd in standard Croatian in this context.

What case are kruh and voće in here?

They are both in the accusative singular as objects of the preposition po indicating purpose.

po kruh – for bread (to get bread)
po voće – for fruit (to get fruit)
The forms happen to look the same as the nominative singular, but here they function as accusatives.

Why is voće singular in Croatian when English uses plural “fruit” / “fruits”?

Voće is a collective neuter singular noun, meaning “fruit” as a mass or category.
So voće can refer to one kind or many kinds of fruit, like English mass noun “fruit” (as in “I eat a lot of fruit”).
If you want to talk about individual pieces or kinds, you can optionally use words like plodovi (“fruits, produce”) or voćke (“fruit trees / pieces of fruit”), but voće by itself is the most common.

Can I say kruhovi in this sentence, or must it be just kruh?

In po kruh, kruh is used as a mass noun, like English “bread”, and that’s the natural choice here.
Kruhovi is the plural (“loaves of bread”) and is used when you explicitly talk about separate breads:

Kupio sam tri kruha / tri kruha. – I bought three loaves of bread.
But for the general idea of going to get bread, po kruh is the standard expression.

What tense and aspect is idem, and why does it mean something habitual here?

Idem is the present tense of the imperfective verb ići (“to go”).
The Croatian present of an imperfective verb can express:

something happening right now, or
a habitual, repeated action.
Because the sentence includes subotom (“on Saturdays”) and često (“often”), the context makes it clear we’re talking about a regular habit, not a one-time action.

Why is there no comma after Subotom ujutro?

Short time expressions like Subotom ujutro are usually not separated by a comma from the rest of the sentence.
You would use a comma if the introductory phrase were longer, more complex, or parenthetical, but simple time, place, and manner adverbials at the beginning typically don’t take a comma in standard Croatian.