1. What does it mean?
쫄다 is a familiar informal spelling used for shrinking back in fear or losing confidence. 쫄았어 describes having been intimidated, while 쫄지 마 tells someone not to be scared.
Also written or said as jjolda
2. The nuance
쫄지 마 can encourage a friend, but 너 쫄았냐? can be a taunt. It is different from 졸다 meaning to doze off; context and spelling help distinguish them.
3. Examples
“면접장 문 앞에 서니까 갑자기 쫄았어.”
Standing outside the interview room suddenly made me nervous.
“처음 하는 발표라도 너무 쫄지 마. 연습했잖아.”
Don't get too intimidated by your first presentation. You've practiced.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.