Making your pattern accessible means youre making your patterns as widely understandable as possible.
Firstly, you're going to want to initially make your pattern in either Word or Google Docs, make it accessible in that program, and then export it to a PDF if you so choose.
This process is the easiest to avoid most problems caused by these formats.
To do that, lets establish a baseline for how to make your content accessible.
Online content, including digital documents, need to follow POUR: Percievable, Operable, Understandable, Robust.
To make your content percievable you need to make sure the information in your patterns can be understood by everyone. This is done by making sure the information is able to be read by screen readers, and by adding alt text and long descriptions to images.
This means that someone can operate and use your content. In digital documents this means making sure that your information is set up properly so that it will be operable with a screen reader or just a keyboard.
This is when information being presented to a user is able to be understood by the user. For crochet patterns this commonly means writing out what row each instruction takes place at.
To make a digital document robust is to make sure it is made so that anyone now or in the future can access it, be it by sight or with a screen reader.
I would suggest following the order this lesson is set up in, from top to bottom. Theres a handy-dandy navigation bar on the side for quick reference as well if this isn't your first time working through a document but you still want some guidance.