Odds are good that you've seen references to accreditation while looking for schools -- something like "University of X is fully accredited by the Upper Northern Montana State Accreditation Commission." Sounds good, but what does it really mean?
Accreditation is basically a process for ensuring that schools meet a certain set of standards. To become accredited, a school is reviewed thoroughly over the course of several years by an external agency that checks that the school meets accepted standards (that it has adequate funds and resources, provides a basic level of education and services who can write my essay for me cheap, etc.) and then makes a decision as to whether the school meets those standards.
There are two types of accreditation: institutional (applied to entire schools, colleges, and universities) and specialized (typically for departments or schools within a college or university). Since accreditation is such a rigorous and expensive process to complete, it has become an important way to differentiate between legitimate schools and fly-by-night operations or "diploma mills" as they're often called (the kind that advertise "Pay $500 and get your PhD in just one month!").
Earning a degree from an accredited school means that other schools and employers will recognize your degree as being valid. Can you imagine spending your time and money at an unaccredited school and then, after all is said and done, having no one take your degree seriously because of the school it came from? Having an accredited degree is particularly important in specialized fields -- such as medicine, law, etc. -- where schools are accredited by very specific agencies who set common standards (for instance, the Commission for Dental Accreditation for dental schools).
Unfortunately, though, you can't take a school's word on its accreditation status at face value. For instance, some schools aren't accredited for a number of reasons -- not just that they're shady or illegitimate. Since accreditation is a voluntary process, not all school's submit to it; some religious schools have philosophical reasons for not pursuing accreditation. In addition, accreditation can take years -- so a relatively young school may not have had time to complete (or even start) the process.
Making matters more cloudy is the confusing issue of accrediting agencies. Most of the confusion stems from the fact that, while education is centralized and controlled by the government in most countries, it isn't in the United States. Accreditation in the U.S. is performed by private agencies, not the government. As a result, it can be tough to determine what is or isn't a legitimate accreditor. Sure, a school might say it's accredited by the "Upper Northern Montana State Accreditation Commission" -- but what if that accreditor isn't legitimate (or doesn't even exist) itself?
In the end, the most important thing for you, the student, to do is to ask questions. Find out if the school you're looking at is accredited, by whom, and then look into the accrediting agency to double-check that they're on the level. If you discover that your school isn't accredited, find out why they aren't. Are they currently being evaluated? Were they turned down? Why? Remember, the value of your degree could hinge on your school's accreditation -- don't risk it.