Sage was created to make your life easier as a WordPress developer, and it contains a collection of valuable tools for creating better websites even faster.
But, much like most new skills it is usually easier to start with the basics, and then get more complex.
What you should know first
If you are just getting started with WordPress, there are some core concepts that you should get a good handle on before introducing anything more complex than the basic files and functions required for a WordPress theme.
Sage often builds on (and sometimes cleans up) the default functionality of these concepts, so knowing how they work will help you be efficient and successful when using Sage.
The WordPress template hierarchy
Before adding any complexities to the file structure that WordPress uses, you should understand how the WordPress template hierarchy works. A large percentage of the Roots Discourse threads are simply people trying to understand this WordPress concept and confusing it with the theme wrapper layer that Sage adds.
Loops & content functions
Writing a WordPress query and loop is something that you should know how to do properly and learn from the Codex. Understanding the role and purpose of each function is essential to writing your own templates and interacting with post data.
Template parts are an often underutilized core part of WordPress that Roots utilizes and expands upon.
Where to start
Well, that depends on your background and the way you learn. It might take you a weekend, a few weeks, or longer to get the basics of WordPress down.
New to HTML, CSS and PHP
If you are new to development as well as WordPress, then your best bet is to start in the Codex and build out the required theme files from scratch at least once.
Developer new to WordPress
When to add in Sage
Don't forget that Sage builds on these core concepts and doesn't break them. Go to the WordPress Codex with questions first, then check out the Roots blog/tutorials, and finally come join us in Discourse when you have any Sage related questions, issues or ideas!