VS + 고 있다

Verb Stem + 고 있다: to be doing ~, progressive form.

This is the progressive form, and it is extremely common. This conveys the sense of something ongoing, incomplete but yet to be completed. It is not used for something that someone does out of habit or consistently or that will never end. That is reserved for the present tense.

This is composed of two basic parts. VS + 고 (and) + 있다 (to be / exist). These two forms suggest that the actor does something and is currently at that point. This is the way that Koreans think of this form, so you may see something like "공부하고, 생각하고, 읽고 있다" which means, "to be studying, thinking, and reading." You may also see 있다 replaced with honorific 계시다.