Any guides to help me get started with Canvas in Salesforce? Need to use it for an Iframe replacement and the guides I have read feel like they skip a big section of how to use it.
Best way us to go step by step through this documentation https://developer.salesforce.com/docs/atlas.en-us.platform_connect.meta/platform_connect/quick_start_simple_create_app.htm
In short : on your heroku app you need to implement code that will act on POST request to your controller and get Signed Request decrypted.
You need to use decrypted signed request to organize interaction between Salesforce and external app via browser side JS. - Canvas App is not a good solution to iframe internal org pages.