There's lots of confusion over what you need to do before you can start developing on the Office platform so I'd like to clear it up here.
You need an Office 365 developer account. Sign up here for a 30 day free trial. It costs $99/year thereafter.
Note: If you are an MSDN subscriber (with Visual Studio Premium or Visual Studio Ultimate), you can get this developer account for FREE.
This post will show you a clear, step-by-step walkthrough of how to register for an Office 365 developer account.
First you enter your personal details:
Then you tell Microsoft what you want your tenant domain and username to be. Office 365 is aimed at enterprises, so imagine a situation where a company A has its own in house developer named B. So in this case, the tenant domain will be @companyA.com and theusername will be developerB. So developer B's login account to Office 365 will bedeveloperB@companyA.com. In this case because you are signing up for a free trial Microsoft doesn't have domains like ____.com to give away. You have to use _______.onmicrosoft.com but you can later associate this to your own domain.
The next step is a verification step:
Enter the verification code you receive:
Wait a few seconds while your account gets created:
Your account is created.
You will receive an email with your tenant domain and username. This is handy information in case you forget. Note that my user ID is firstname.lastname@example.org - this is a completely different sort of account from a ABC@outlook.com/ABC@hotmail.com type of account. The former is an Office 365 tenant account where the latter is a Microsoft account. Think of the difference as the former being an enterprise log-in that you use at work, and the latter being your own personal account that you use for Bing, Outlook.com, and all of Microsoft's consumer services.
Now when you click on "Access your Office 365" in that email, or if you click on "You're ready to go..." in that registration screen, you get to this:
And there you have it! You've set up a developer account for Office 365.
If any of the "tile" icons representing Word Online, Excel Online, PowerPoint Online, OneDrive, Sites, Outlook, Calendar or People are grayed out, that means these services haven't finished provisioning yet. Give them a few more minutes, and when you refresh, they should be ready to use.
That's all you need to start using O365 APIs!