Modal verbs in Croatian express obligation, ability, need, desire, and permission. Morati means "to have to" or "must," as in moram ići (I have to go). Moći means "can" or "to be able to," so ne mogu doći translates as "I cannot come." Trebati means "to need" or "should," appearing in trebam pomoć (I need help). Htjeti is the straightforward "to want," used in hoću vodu (I want water). Smjeti means "to be allowed to" or "may," and its negative is very common: ne smiješ pušiti ovdje means "You must not smoke here," where "must not" really means "are not allowed to."
When you want to make a polite request, the conditional form of htjeti is the standard. A man says htio bih and a woman says htjela bih, both meaning "I would like." A typical sentence is htio bih kavu, molim (I would like a coffee, please). To ask whether someone is willing to do something, build a question with hoćeš li plus an infinitive: hoćeš li mi pomoći, molim te? means "Will you help me, please?"