A 'post-doc' is a position you get in academia after your ph.d. thus the name.
After you get your ph.d. you look around for post-doc positions, just like you would any other job really.
It's really a continuation of what you were doing before, you do research as you did as a graduate student, paired with an established faculty member who helps arrange funding, networking, and helps channel your talent (hopefully). The difference is you tend to be more of on a peer basis, than a subordinate advisor-student role, and have more independence, and are expected to really help with all their efforts to get funding and network, rather than observe and gratefully recieve the benefits
. Essentially you work with them (instead of under them), and use their resources to publish more papers.
From what I gathered from friends when I was in graduate school it usually takes 2-3 post-doc positions, lasting about 2-3 years each (i.e. a decent length of research for a good paper) before you have a solid chance at landing a 'real' academic position, where you're a full professor or research scientist.
So, just to let you know, you spend 4 years (at least) getting your B.S., about 5 years (at least) getting your Ph.D. and another 4-9 years as a post doc before you land a tenured, secure academic researching/teaching job. So, assuming you started college at 18, you'll be 31-36 years old, on average, before you find any real job security..wait, you still have to get that tenure, another 2-4 years or so..., so you could be 40 before you find job security...there's a reason Tenure is so highly valued at colleges.