As a noun, a while refers to a period of time. When you say a while back or a while ago it means some time ago or at a time in the past.

1. It's not that long since I saw my brother. It was just a while ago when we met for lunch.
2. I finished my assignment a while back. So now I can relax.

1. I was talking to John about GDPR training, but that was a while ago. We should revisit that idea.
2. My first job was with an Events Organization company, but that was a while ago - almost seven years now.