"Il" and "Ils" sound identical. But by listening carefully to the verbs, you can figure out the pronouns. So "Il boit" (bwah) versus "Ils boivent" (bwavv). Similarly, "boit" and "bois" sound identical. So you have to hear the pronoun and know which of the conjugated verbs goes with which pronoun.
The intonaton. Statements are flat or goes down at the end of the phrase. Questions rise at the end of the phrase.
In some cases the word order is reversed in questions, or include words as who, why, which one/s et cetera, but the most important feature ro recognise a question is the rise.