This pattern is indicates a habitual action.

- used mostly with action verbs
- used in the present tense, indicates something someone does on a semi-regular but infrequent basis
— when used in the present tense, often used with the words 까금/from time to time or 이따금/occasionally
- when used in the past tense, it means "one used do do every now and again" or "every once in a while"
- is a contracted form of 고는 하다

Examples:
그 사람은 예전에 자주 놀러 오곤하더니 요즘에는 통 안 온다./That person used to come often to play (to hang out and have fun, have fun) often but these days he/she doesn't come at all.
작년에 가끔 군산에 가곤 했어요./Last year I used to go to Kunsan occasionally.