Learn Hardcore Croatian: Kad budem skuhala krumpir, dodat ću ga u salatu. - When I have cooked the potatoes, I will add them to the salad.

Kad means when and introduces a time clause: Kad budem skuhala krumpir... = When I have cooked the potatoes...
Kad and kada are very close in meaning. Kad is very common in everyday speech and often preferred in shorter, more conversational sentences; kada can sound a bit more formal or explicit, but both are correct in many contexts.

What tense is budem skuhala? Why not just skuha(m) or skuhat ću?

budem skuhala is the Croatian future perfect–type construction used in a time clause to express a completed action before another future action.
Structure: budem (future form of to be) + past active participle (skuhala)
Meaning here: When I (will) have cooked the potatoes, I will add them to the salad.

Using present (Kad skuham krumpir...) is also common and often sounds natural: it can also mean “when I cook/when I’ve cooked.” But kad budem skuhala is very explicit about completion before the next action.

Why is it budem and not ću biti?

In subordinate clauses introduced by kad, ako, čim, etc., Croatian often uses budem + participle rather than ću + infinitive.
ću biti is a normal future form (I will be), but the pattern for “when I have done X” is typically kad budem + participle.

What does skuhala tell me about the speaker?

skuhala is the feminine singular past active participle of skuhati (to cook/boil). It implies the speaker is grammatically feminine (or speaking as a female).
A male speaker would usually say: Kad budem skuhao krumpir, dodat ću ga u salatu.

Is skuhati krumpir specifically “boil” potatoes, or just “cook” them?

skuhati generally means to cook by boiling (or to cook something “in a pot”/by cooking until done), and with krumpir it usually implies boiling unless context suggests another method. For other methods you might see:

ispeći krumpir = bake/roast potatoes
pržiti krumpir = fry potatoes

Why is krumpir not in plural? In English I’d say “potatoes.”

Croatian often uses a singular mass/collective-like form where English uses a plural. krumpir can function like “potato (as a food item)” or “potatoes (in general/as a portion).”
If you want to emphasize separate potatoes, plural is possible: Kad budem skuhala krumpire...

What case is krumpir here, and why?

It’s accusative, because it’s the direct object of skuhati (to cook something). For masculine inanimate nouns like krumpir, accusative = nominative in form, so it looks unchanged.

Why is the comma there?

In Croatian, a subordinate clause introduced by kad is normally separated by a comma from the main clause:
Kad budem skuhala krumpir, (subordinate clause) dodat ću ga u salatu. (main clause)

What does dodat ću mean exactly, and how is it formed?

dodat ću = I will add.
It’s the future tense formed with the auxiliary ću + infinitive dodati (here appearing as dodat because of a common spelling/phonological shortening when ću follows):

full: dodat ću (from dodati ću)
You’ll also see: dodati ću (less common) and ja ću dodati (more explicit).

Why is ću in second position? Could it be elsewhere?

Croatian clitic words (like ću) typically go in the second position of their clause (after the first “chunk”):

Dodat ću ga u salatu. (first chunk = Dodat)
You can also say:
Ja ću ga dodati u salatu. (first chunk = Ja)
Both are correct; the sentence may shift emphasis depending on word order.

Why is ga used? What does it refer to?

ga is the accusative masculine singular clitic pronoun meaning him/it. Here it means it and refers back to krumpir.
Croatian often uses such object pronouns to avoid repeating the noun: ...I will add it to the salad.

Where does ga have to go in the sentence?

Like other clitic pronouns, ga typically appears near the start of the clause, in the clitic cluster, usually right after the first element and next to ću:

Dodat ću ga u salatu. (very natural)
Other possible orders exist with emphasis, but placing ga next to ću is the default you’ll see most often.

Why is it u salatu and not u salati?

After u, Croatian uses:

accusative for motion/direction (into)
locative for location (in)

Here, add into the salad implies direction/goal → u + accusative: u salatu.
If you meant “in the salad” as a location, you’d use locative: u salati.

Is salatu definite or indefinite? How do I know if it’s “the salad” or “a salad”?

Croatian has no articles (“a/the”), so definiteness comes from context. In many everyday contexts, u salatu will be understood as into the salad (the one being prepared). If you need to be explicit, you can add:

u tu salatu = into that salad
u jednu salatu = into a (one) salad

Could I replace Kad with Čim or Nakon što? Would the grammar change?

Yes, with slightly different nuance:

Čim budem skuhala krumpir, dodat ću ga u salatu. = As soon as I’ve cooked it... (more immediate)
Nakon što skuham / nakon što budem skuhala krumpir... = After I cook/have cooked...

These connectors still commonly pair with the same kind of future-in-a-time-clause structure, though nakon što + present is also very common.

Is this sentence more “spoken” or “written”? Does it sound natural?

It’s natural and correct. The choice kad budem skuhala can sound a bit more careful/explicit than the very common everyday Kad skuham krumpir, dodat ću ga u salatu, but both are normal Croatian.