Accessibility is intended to ensure the world works for the widest possible audience. This means that any item, tool, or web element can be accessed by everyone, including those with differing abilities that may require additional elements to ensure access.
Accessibility is for everyone. Ensuring anything a person creates or modifies is accessible has the added benefit of helping everyone. A created object can help people of differing abilities in unexpected ways.
There are currently four self-guided tutorials available.