It's used inflectively to make -ing words.
-ing is a morpheme that is typically acquired fairly early by English language learners and usually without any accuracy issues.
Pronunciation[edit | edit source]
-ing is generally pronounced /-ɪŋ/. /-ɪŋ/ may be further reduced to /-ɪn/ in unstressed syllables colloquial speech, but not stressed syllables. Historically the pronunciation was /-ɪŋg/ and this is still to be found in some parts of Northern England and the English Midlands - see singer-finger split. Some speakers in Northern England devoice the /g/ to a /k/, to make /-ɪŋk/ making "something" sound like "some think".