Learn Croatian: Moramo raditi u skladu s uputama. - We must work in accordance with the instructions.

Complex prepositions end with a standard preposition that determines the case. Since u skladu s ends with s (with), the noun that follows it must be in the instrumental case. Here, that gives us the instrumental plural uputama.

What does the skladu part of u skladu s actually mean?

It comes from the masculine noun sklad, which means "harmony", "order", or "agreement". So literally, the phrase translates to "in harmony with". Here, skladu is in the locative case because it follows the preposition u (in).

Why do we use s instead of sa before uputama?

You only need the longer form sa when the next word starts with a sibilant consonant (s, z, š, ž) or a tricky consonant cluster. Since uputama starts with the vowel u, the short form s flows perfectly well.

Is there a simpler way to say "according to the instructions" without using u skladu s?

Yes, you can use the preposition prema (according to), which takes the dative case. You would say prema uputama. The word uputama looks identical here because dative, locative, and instrumental plural endings are the exact same for this noun group, but the grammar behind it is different. U skladu s sounds slightly more formal, just like "in accordance with" vs. "according to" in English.