Databases provide persistence to data. When the user sends data -- let's say a new product listing -- we read the data from the request and hold it in memory while we validate it or process it in any other way. But once we send the response, it will be erased from memory, lost forever unless it is stored somewhere else.
ActiveRecord is a method to deal with data that represents something, like a a new product. We model it by listing its attributes (price, color), validate