I'm interested in doing a PhD so that I will be able to work more independantly and have more input on the projects I work on. However, I am not interested in pursuing a career in academia and would like to work in industry. I keep hearing about people finishing PhDs and going on to do postdocs, etc. but I don't understand what these are, and is this the only route you can really take after a Phd? I'm afraid of ending up overqualified for what I want to do?

I'm considering doing a science PhD but would like to know why people undertake PhDs and what they hope to get out of them? I'm also concerned about being overqualified for jobs I may be interested in once having a PhD?