Evernote is a note taking and note syncing application and DropBox allows you to access files inside it across all your devices, so you could access documents stored inside DropBox on you Mac and then open them on your iPad.
I use Evernote on my iPad to take down quick notes and then when I get home I'll use evernote on my Mac to organize my notes and tag them. Because Evernote syncs via the cloud automatically anything you add on the iPad version automatically downloads to the Mac/PC version.
I keep all my course related files stored in DropBox that way I can gain access to them on my iPad. Dropbox is kinda like a flash drive in the cloud, you put files into it from one device and it will automatically download to all your others, great when I need to work on a report on one of the crappy school pc's when I've left my Mac at home.