Start by following the guide from start to finish. It's really clear and written by Evan, Elm's author. Do the exercises!
I found this example helpful as an example of piecing everything together after reading the guide
Don't worry about modules or splitting stuff into separate files. This advice is oft repeated in the Elm community and it's absolutely correct. The patterns that work in Elm aren't the patterns that work in other languages, and if you split modules out too early you'll make it harder to get a sense of the right module abstractions. Refacting is a breeze so you can modularise later. (See /The life of a file/ below).