Phrasal verb is a group of words that is used like a verb and consists of a verb with an adverb or preposition after it, for example 'set off' or 'look after'.
More often than not, a phrasal verb has a complete different meaning with its independent components, such as "set" and "off" vs "set off(to start to go somewhere)", "look" and "after" vs "look after(to take care of someone by helping them, giving them what they need, or keeping them safe)". So, different/same verbs with different prepositions/adverbs convey different meanings. There is no short cut or rule in mastering them all, and you have to learn them one by one by rote.
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