1. What does it mean?
셀카 is a shortened form of 셀프 카메라, a Korean expression using English 'self' and 'camera.' It names a photo someone takes of themself.
Also written or said as 셀프 카메라, selfie, selca, 셀피
2. The nuance
셀카를 찍다 means to take a selfie, and 셀카봉 is a selfie stick. A photo can be a 셀카 without heavy editing or a particular pose. If another person takes your portrait, 사진 is more precise than 셀카.
3. Examples
“여행 첫날에 숙소 앞에서 셀카를 찍었어.”
I took a selfie outside my accommodation on the first day of the trip.
“셀카 말고 풍경이 더 많이 나오게 사진을 찍어 줄래?”
Instead of a selfie, could you take a photo of me with more of the scenery in it?
Sources
KoreanClass101: Korean language lessons
References support the meaning and usage. Example sentences are written for NoCapWiki.