It’s a friendly way to invite you to open up and talk about yourself. It’s not a serious question.

They're asking about your recent activities. It could be things you've been doing at work or in your leisure time. Time is always relative, so "lately" could mean different things depending on who's asking you the question. To someone you see frequently, "lately" could mean in the last few days. To someone you see less frequently, "lately" could mean the last few weeks or months.