Regarding hash key and value mapping

I couldn't get the hash value well, so I looked it up and found that it was a bit overlooked.

hash1 = {key: "value"} #=> {:key=> "value"}

When,

hash2 = {"key"=> "value"} #=> {"key"=> "value"}

Did not understand the difference. It seems that the key name changes depending on how you write it. In the above example

hash1["key"] #=> nil
hash1[:key] #=> "value"

become.