Phrasal verbs 4 - on/off (1)

Why do you need to know when to use 'on' or 'off' as part of a phrasal verb? And what IS a phrasal verb?On and off are often used with a verb. To sound more like a native speaker, it is useful to know some of the times when this is so!A phrasal verb is a combination of two or three words that have a special meaning when used together. They consist of a verb and a preposition.