Aphasia is the reason ExpressAgain exists: the person can think, read and understand, but the words will not come out. The app's core library, the Learn courses, Practice Out Loud and the family circle were built for it first, and the Aphasia and Stroke mode is the core library every other mode builds on. More about aphasia, on the public site, explains it in plain words, with eight pages that each answer one question people ask (see Understanding aphasia: plain-language answers).
The condition page on the public site tells the full story and ends with the way to create an account.