Here is how I'd suggest you learn SEM:
#1 - Open a Google Adwords Account (You can search for free credit / promo codes) online and play around with it.
#2 - Review all of Google's training material: https://support.google.com/adwords/?hl=en&page=examstudy.cs#topic=3119071
#3 - When you finish Google's training materials, then read about Adwords on the web. Here is one good resource and you can Google for more:
#4 - Sign up for an affiliate network (e.g. Commission Junction or Linkshare) and use your free credit to promote another company's offer.
#5 - Once you feel comfortable with Adwords, consider building out your own Lead Gen websites or selling leads to existing affiliate networks (e.g. Motive Interactive or Integrate.com)
#6 - If you'd like to learn from someone else, find an entry-level job at an agency: http://www.indeed.com/q-PPC-entry-level-jobs.html
#7 - Another good way to get good at PPC if you work in an in-house marketing role is to hire someone to audit or manage your own account for a period of time so you can learn how they think and what they do.
#8 - One word of caution: Google takes a minute to learn and a lifetime to master. Their default settings make it very easy to waste a lot of money so really make sure you know what you are doing before you spend too much money.