According to Krashen, there are two ways of developing language ability. 

Acquisition involves the subconscious acceptance of knowledge where information

is stored in the brain through the use of communication; this is the process

used for developing native languages.  Learning, on the other hand, is the

conscious acceptance of knowledge ‘about’ a language (i.e. the grammar or

form). Krashen states that this is often the product of formal language

instruction.