What is a phrasal verb?

A phrasal verb is a verb which is a combination of a verb and an adverb, a verb and a preposition, and a verb with an adverb and a preposition. It can have a literal meaning that is easy to understand because the meaning is clear from the words that are used in the phrasal verb itself. It can also have an idiomatic meaning which cannot easily be understood by looking at the words themselves.

The following examples contain a literal meaning and an idiomatic meaning:

Verb and Adverb (run + around) to run around (something) - to run in a circle around something
The dog ran around the fire hydrant.
to run around (somewhere) - to go to various places to do something
I spent the day running around downtown.

Verb and a Preposition (run + into) to run into (someone or something) - to hit or crash into someone or something
The car ran into the truck on the busy street.
to run into (someone) - to meet someone by chance
I ran into my friend in a restaurant yesterday.

Verb and Adverb and Preposition (run + along/around + with) to run along with (someone or something) - to run beside or at the same pace as someone or something
The dog ran along with the bicycle.
to run around with (someone) - to be friends and do things with someone or with a group
The boy is running around with a bad group of people.

Some idiomatic expressions are made with a phrasal verb plus some other words. These words are used in a fixed order to give an idiomatic meaning.
to run (verb) around (adverb) like a chicken with its head cut off - to run around with what seems to be no purpose
I ran around like a chicken with its head cut off as I tried to prepare for my holidays.