BOY it is boring as fock who wanna talk

Explain what has to happen when you use être instead of avoir for the formation of the passé composé? il an english explanation with steps if possible

Anne mange un sandwich aujourd'hui?

Fill in the blank with the correct adverb of frequency: je (never eat) a la pizzeria a: ne mange jamais b: ne mange souvent c: ne mange rarement d: ne manges de temps en temps