Advertising and marketing is a wide field. An undergraduate degree in business might be enough to get you started in certain lines. A good liberal arts background with an MBA in advertising might be required in others.

AnswerIn advertising, the book is king. Never, ever call it a portfolio. No one in advertising calls it a portfolio. It is ALWAYS a book. In it you put samples of your work. The best samples are ones cut out of magazines or newspapers--this shows that your work was good enough to be published. These are called "tear sheets" although you don't actually tear them out. If you do sales sheets or other printed collateral that wouldn't have been published in magazines, those can go in too. If you can get contract proofs (also called Matchprints or Chromalins--those are two popular brands of contract-proofing material) of your work, that would be fine too. Laser prints should only be in your book if you don't have anything else--they show you're new talent, but if you really ARE new talent, that's okay. (I have to update this for modern reality: Matchprint, WaterProof and Chromalin proofs were made from film negatives. These days, printing plants use computer-to-plate systems and those proofing systems are no longer made. Now, all proofs are made on inkjet printers. So, if you have color contract proofs that's what you'll get.) Once you've been in the business a few years, you'll have enough tear sheets that you won't need lasers or Matchprints. Most of us only have twelve pieces in our books--fewer than that shows you're a newbie, more than that takes too long to go through.

The equivalent of a book for television and radio is the reel.

Update your book as time goes on to keep it fresh--with very few exceptions, no one wants to see an ad that's ten years old. The exceptions are if you create a really memorable campaign--I'm certain Richard Trentlage still has "The Wiener Song (I Wish I Was An Oscar Meyer Wiener)" on his reel.

As far as education goes, every decent-size town in America has at least one advertising agency and you might be able to get a job with a very small one with just a book...but if you want to work for a midlevel agency or for one of the "worldwide" ones like BBDO, DDB or J Walter Thompson, you'll need at least a bachelor's in advertising.