Disneyworld is Disney's original theme park complex in Orlando, Florida. Disneyland is in Anaheim, California. I've never been to Disneyland, but having grown up in Florida, I've been to the various parks within Disneyworld many times. It's a lot of fun for kids, not so much for adults (unless you're the kind of adult that holds the Disney brand in some sort of saintly regard, and let me tell you, there are plenty of them). They do have a couple of decent roller-coaster type rides, at least.
If you do go to the Orlando location, definitely go in the spring or fall; summers in O-town are unbearable, and winters can be downright chilly for wimpy, coast dwelling Floridians.
Walt Disney World is one of my favorite places to go. Walt Disney purchased the land for WDW because he saw what happened to the area surrounding Disneyland -- business development immediately surrounded the park and left no room for expansion or any kind of buffer zone. Walt figured if he bought enough land, he could develop it as he saw fit without worries of overcrowding.
Walt Disney World consists of four main theme parks: Magic Kingdom (which is quite similar to Disneyland), Epcot, Disney-MGM Studios, and Animal Kingdom. The resort also has several golf courses, three water parks (one of which is closed for the foreseeable future), a campground, and Downtown Disney (a shopping area which also contains a Cirque de Soleil troupe and DisneyQuest, an indoor virtual-reality park).
I've been to WDW in all four seasons; if you're accustomed to heat, summer is just fine, as long as you pace yourself. Avoid the US holidays like Memorial Day or Labor Day, because the Florida residents tend to come to the parks on those weekends, especially if it involves a school holiday. Christmas is the most popular and most expensive time to go, while January, February, and September are usually the least crowded.
WDW's site is here( http://disneyworld.disney.go.com/wdw/ind... while Disneyland's site is here( http://disneyland.disney.go.com/disneyla... ). There are also several good guidebooks you can purchase, and I highly recommend obtaining a couple of them before your first visit, especially if you're coming to Disney World, because the place is simply too large to see everything -- you have to do some prioritizing and planning, and the guidebooks are a great help. Do an Amazon search for 'disney world guide' for suggestions.
There's a weekly podcast, from a guy who lives in Orlando, that covers just the Orlando parks; you can find it here( http://distantcreations.com/insidethemag... ). He doesn't work for Disney, but he's definitely a fan, and often gives some good information.