Prerequisites

You need the appropriate access and tools to complete the quick start steps.

Access to a Developer Edition organization.
If you are not already a member of the Force.com developer community, go to developer.salesforce.com/signup and follow the instructions for signing up for a Developer Edition organization. Even if you already have Enterprise Edition, Unlimited Edition, or Performance Edition, use Developer Edition for developing, staging, and testing your solutions against sample data to protect your organization’s live data. This is especially true for applications that insert, update, or delete data (as opposed to simply reading data).

If you have an existing Developer Edition organization, and, from Setup, you don’t see the menu item Canvas App Previewer, contact Salesforce.
“Customize Application” and “Modify All Data” user permissions. If you’re an administrator, you most likely already have these permissions. Otherwise, you need to add them so that you can see the Canvas App Previewer and create canvas apps.
A Heroku account. Go here to create a Heroku account: https://api.heroku.com/signup.

Force.com Canvas Developer's Guide