Not quite sure how to get started? No worries -- let's take a look at everything you'll need to turn your iPad into a full-fledged Office companion.
First up: an iPad. The Office apps are compatible with any iPad that can run iOS 7, which, alas, leaves out first-generation models.
Second, if you want to create and edit documents on your iPad, you'll need a subscription to Microsoft Office 365. Without one, you'll be able to view Office documents, though you can do that already with any number of third-party apps.
Office 365 Home Premium (soon to become just "Office 365 Home") costs $9.99 monthly or $99.99 annually, a price that includes five PC and five tablet licenses. The forthcoming Office 365 Personal ($6.99 monthly, $69.99 annually) will give you one PC and one tablet license.
The apps themselves -- Word, Excel, and PowerPoint -- are free (as is OneNote, which debuted for iPad in late 2011). They're installed individually, meaning you don't have to use the entire suite if you don't need to. Let's walk through using Microsoft Word for iPad (the process is virtually identical for Excel and PowerPoint).
First, download and install Word for iPad from the App Store.
Start the app, then swipe through the introductory screens until you reach the last one. Here you can skip the sign-in process (which you'll have to do if you don't have an Office 365 sub) or type in your subscription email address and password. For our purposes here, I'll assume you've done that.
Open existing documents
Signing into your account automatically links Word to your Microsoft OneDrive, so if you tap Open and then the name of that drive, you'll see all the folders you have there: Documents, Public, and so on.
For a list of documents stored on your iPad (there probably won't be any at first), tap iPad. You can also tap Add a Place, but unfortunately Word doesn't support any third-party services like Dropbox or Evernote -- your only available cloud services are OneDrive and SharePoint.
Nevertheless, opening a document couldn't be much easier: Tap one of the folders for a list of the items stored there, then tap any Word file to open it.
Create new documents
To create a new document, tap the New icon, then choose from the various options: blank document, brochure, invoice, proposal, etc.
After you've worked on it a bit, you might go looking for a Save option. There isn't one; rather, you tap the Back arrow at the top-left corner of the interface, and that brings up a Save As field where you can provide a name.
You can also choose where this document should be saved: OneDrive or on your iPad proper. If you choose the latter, you can always migrate it to the cloud later on: While viewing the Recent or Open menu, tap the up-arrow icon next to any document, and then tap Move to Cloud.
If you don't want to back out of editing just to perform that initial save, tap the File button (which is one icon to the right of that Back arrow). Here you'll see that AutoSave is turned on by default (handy!), plus a Name field you can tap in lieu of "Save As."
There's also a Duplicate option here (grayed out until you save the document at least once), helpful if you want to create templates or the like.
Share your document
There are a couple ways to share files. First, while viewing any file list (in the Recent or Open menu), you can tap that aforementioned up-arrow icon to reveal a Share option. From here you can email the document as an attachment.
If that document is stored on your iPad, that'll be your only sharing option. But if it's stored on OneDrive, you'll also see "Email as Link" and "Copy Link."
These same options are accessible within any open document by tapping the little Share icon in the top-right corner of the interface.
Most everything else within Word for iPad (and Excel for iPad and PowerPoint for iPad) is self-explanatory, especially if you've used the desktop and/or Web versions of the programs. It's an admirably simple app, yet it contains all the basics most users are likely to need on the go.