Learn Croatian: Hoćeš li probati sladoled? - Do you want to try the ice cream?

In Croatian, a sentence cannot begin with a short (clitic) word. Since the verb is the very first word in this question, we have to use the full form hoćeš. If you tried to say ćeš li, it would be grammatically incorrect!

What is the word li doing in this sentence?

li is a question particle used to form yes/no questions. When you put the verb at the beginning of the sentence to ask a question, you follow it immediately with li. Together, hoćeš li translates to "do you want?".

Why doesn't probati change its ending to match "you"?

probati is in the infinitive (the dictionary form, meaning "to try"). Just like in English ("Do you want to try?"), when you use a verb of wanting like hoćeš, the action that follows stays in the infinitive form.

I thought direct objects take the accusative case. Why didn't sladoled change its ending?

sladoled actually is in the accusative case here, because it is the object you are trying to eat! However, because it is a masculine noun that is inanimate (a thing, not a living being), its accusative form looks exactly the same as its nominative (dictionary) form.