We often not do one thing at a time, but we do many things at the same time. However, currently, you might not know how to put that in Korean words. However, indicating you did something while doing something else at the same time is not difficult at all because you just need -(으)면서 for that.
The Korean time expression -(으)면서 is a simple Korean grammar form you can use to indicate that while you were doing one thing, you were also doing a second thing. So it indicates that actions take place simultaneously. This is, of course, easy to understand.
가: 왜 안 자요? 내일 큰 시험을 볼 거예요.
나: 공부하면서 커피를 많이 마셔서 못 자요.
A: Why aren’t you sleeping? You are going to have a big test tomorrow.
B: I can’t sleep because I drank a lot of coffee while studying.
How To Use
Attaching the ending -(으)면서 is not difficult at all. As you can probably guess, it follows the same pattern as the conditional form -(으)면. So it is a verb ending that follows the ‘batchim/no batchim’ rule. If the verb stem ends in a batchim (consonant), you have to use -으면서. However, if it ends in no batchim (vowel), you use the form -면서. Take special care for the ㄹ irregular verbs, because the ㄹ is treated as if it were a no batchim. However, this is not the case for the ㄹ that appears during the ㄷ irregular verb conjugation! Don’t end up neglecting the other Korean irregular verbs though.
Besides the conjugation, there are a few rules you need to keep in the back of your head in order to properly use the Korean time expression -(으)면서. First, the subject of both clauses needs to be the same. You cannot use -(으)면서 when the subject of the first clause is different from the second clause. For those situations, you can use 동안. Lastly, sentences with -(으)면서 are always written in the present tense. Even when you are talking about the future or past, you need to use the present tense.