Learn Hardcore Croatian: Stol je čist.

Stol: noun, masculine singular, nominative; the subject (“table”).
je: 3rd person singular present of biti (“to be”), an enclitic; the copula “is.”
čist: adjective “clean,” masculine singular nominative; a predicate adjective agreeing with the subject in gender and number (and in nominative case).

Why is there no article like “the” or “a” in Croatian?

Croatian has no articles. Context supplies definiteness or indefiniteness. Stol je čist. can mean either “The table is clean” (most common reading in context) or “A table is clean,” depending on what you’re talking about.

What case is stol in here, and when would it change?

It’s nominative because it’s the subject. Other common forms:

Genitive: stola (e.g., “nema stola” – “there is no table”)
Dative/Locative: stolu (e.g., “pri stolu,” “na stolu” – “at/on the table”)
Accusative: stol (e.g., “vidim stol” – “I see the table”)
Instrumental: stolom (e.g., “sa stolom” – “with the table”)

Why is the adjective čist masculine singular?