You should probably start with the fairly comprehensive wikipedia article. The basic idea is that one or more plaintiffs go to court, showing both an injury (in the legal sense of being worse off through a tortfeasoer's action or inaction), and the existence of a large class of 'similarly situated' plaintiffs. The class of deaf people would easily fit that description - deafness is something that's easy to define and not very controversial.
If the original plaintiff has standing, a trialable issue exists, and a class of similarly situated plaintiffs can be certified, then a jury trial takes place like it would for any other kind of tort case. If the defendant is found guilty, then economic and/or punitive damages are calculated, the defendant may agree to settle or appeal, and so on. If there is a settlement or award, then lawyers for the plaintiffs make reasonable efforts to contact the other similarly situated plaintiffs (by advertising in newspapers, magazines, or wherever else there's a good chance of reaching those people), who can either opt out of the settlement and preserve an individual right to sue, object to the terms, or do nothing and receive a coupon or some other benefit. Leftover monies that are unclaimed after distribution are usually donated to some charitable organization. Having a plan in place for the distribution and disposal of any settlement or award is one of the necessities for class certification.
Obviously, I am giving you a ridiculously simplified summary here. Entire books can be written on this subject. Class actions can be frivolous or abusive in some cases, but in general they are a good thing because otherwise it would be uneconomical for individual plaintiffs to sue as the cost of going to court would exceed any award they could possibly win, and so tortfeasors would have no incentive to accomodate their requests or settle with them.