GRE test is available in more than 1000 test centers. It is a test known taken throughout the year.
1) Before you register for the test you need an ETS Account, Make sure you have read all important things about name that you will be registering and what to do if thee is a name change
2)Pick your type of test,Whether you want a pen paper based or computer based.
3)Take a look at the list of test centers and pick the one that works the best for you
All the best!