Wow, this is a pretty big question. I think the first thing to understand is that Canvas isn't really a content supplier, it's a system for managing learning. What that means is they give you a place and the tools to turn your content into a fully fledged, online course to provide to your students. Here's a 90 second intro to what this is: Get to know Canvas on Vimeo
You can try it out for free at the Free For Teachers Canvas, where you can build a course and even invite students to attend. Sign up for an account here: Create a Canvas Account
As far as costs, that's highly variable depending on what features you want, what your school's IT department is capable of doing, and how big your school is. Instructure does offer a turn-key solution for a price, or your school's IT department can host Canvas for free (but will need some decent infrastructure and staffing to pull off). To contact Instructure, email firstname.lastname@example.org
If you have specific use cases, or want to know specific information, feel free to ask and someone in the community will see if they can help. Basic information would be how you want to use Canvas, if you're a teacher or admin for your school, and if you want to be fully online, partially online (blended or hybrid), or fully traditional with some online components.
I'll agree that this is a pretty big question! In addition to everything Anthony recommended (which were spot on), here are some additional resources:
Hope these help!