How do I know whether to use al or ai?

How do know when to use quello or quegli or quel? It's very confusing!

Ciao Denise, the prepositions "al" and "ai" are the combination of : the preposition "a" (to) + the article il (the) the preposition "a" (to) + the article "i" (the-pl.) For this reason you will need to use : "al" if the noun following is masculine, singular. Example: io vado al mare (il mare) "ai" if the noun following is masculine, plural Example: l'eredita' va ai figli (i figli) "Quel" and "quello" are the translations of "that" (singular) while "quegli" is the translation of "those". Quello" is used in front of masculine nouns starting with s followed by a consonant, or nouns starting with a z. "Quel" is used in front of the rest of masculine nouns. quel gatto - that cat quello studente - that student I hope this helps Ciao