The following links are to sites with information about the Americans with Disabilities Act (ADA). The ADA is the Federal Law which governs Service Dogs. A couple things you need to know:
A Service Dog is a dog that has been trained to do tasks that help a person with a recognized disability.
There is no such thing as Certification to have or use a Service Dog. You may get a "Trainer's Certificate" from your Trainer, but this is NOT REQUIRED to have a Service Dog!
A Service Dog DOES NOT have to wear a vest or have any kind of identification.
There is no ID Card, or any other kind of paperwork required to have or use a Service Dog.
A business owner or employee may only ask you two questions about your Service Dog. They MAY NOT ask you about your disability!
The information you need from the US Department of Justice (the Federal Agency that enforces the ADA Law) will be found in the links below:
Revised ADA Requirements: Service Animals
Frequently Asked Questions about Service Animals and the ADA
Commonly Asked Questions About Service Animals In Places of Business
Service Animals and Emotional Support Animals | ADA National Network
Frequently Asked Questions
Service Animals and Assistance Animals - HUD
Service Animals - New York State Attorney General
VA Service Dog Info