Ciao Corinne 🙂 la mattina and il mattino are more or less the same, but we use one instead of the other in some specific contexts and in a slightly different way. You’ll memorise naturally which one to use with practice and by listening to a lot of contents in Italian. In general “mattina” is more frequent than “mattino”. With days of the week we prefer “mattina” (Giovedì mattina vado a mare; il lunedì mattina lavoro…). Sometimes we can say “La domenica, al mattino, vado al parco” (but it sounds less natural and it’s used to specify what part of the day you are talking about). Some examples of sentences in which you can use both: “La mattina faccio colazione” – “Al mattino faccio colazione”; “Mi sveglio presto la mattina” – “Mi sveglio presto al mattino”, etc.