For a long time the newspaper classifieds and word of mouth were the only two ways you could find a job without going door knocking. Note that word of mouth is still perhaps the best way to search for jobs, as over 60% of jobs are never publicly listed. As the saying goes, it's not what you know but who you know (and how you manage to use your connections).
If you're like most people, you need to eat. Eating requires money to buy food, unless you're privy to some handy barter scheme, and unless you've won the inheritance lottery you're going to need to work for you food money. Which means you need to find a job. Sure, you could make do walking door-to-door and looking for help wanted signs, but the most efficient way to search for jobs is going to be through the internet.
Ask relatives, past business associates, and friends if they know of anyone who's hiring. This can be especially important if you're looking for a job in a particular field. If you can't score anything by word of mouth, the classifieds may still be worth a read, but many newspapers publish their classifieds online anyway, so an internet search will still make things easier while keeping your options open.
Two of the most-used and therefore most helpful job search sites are http://craigslist.com and http://monster.com. As with most forms of communication, the sites with the most traffic are often the most helpful (it doesn't do you any good to own the only telephone). http://Monster.com and http://craigslist.com have thousands of job posts every day, and both are searchable by geographic locale, employment type, and salary. You can also post your resume and allow recruiters to come to you.
Many other smaller websites allow you to search for jobs in your immediate area or in your area of expertise, though the latter listings are often nationwide. It is important to note that not all internet job postings are what they seem; any recruiter who asks you to pay money before you start is probably running some sort of a scam, pyramid or otherwise.
Imagine if you were to apply for a job in your hometown and the business owner offered to hire you, but first wanted a $5 bill. These internet scams, often billed as "work at home" opportunities, are equally dubious.
However, if you stick to legitimate sites and present yourself as an attractive job candidate, the internet will allow you to search for jobs faster and easier than searching through the daily newspaper with a highlighter.