It's as simple as filling in a form. You'll need a (free) Audition Account, a headshot, and some contact information.
ALL Mediability.pro casting calls are for disabled performers.
To submit, access the Audition form and enter the contact details and images. Include the Call ID (below the title) and the role you're submitting for. If your submitted details match the call, they will be submitted to Casting for consideration. Information is ONLY visible to the Casting Director, and are deleted 30 days after the call closes.