When you take the GRE, you pick what schools to send your results to at the end. If you already took them (or if you're not sure at the time you finish the exam), you can go on their website at any time after that and send them to more schools electronically. You get 4 at no charge if you submit them at the time you take your test, but if you're applying to more than 4 or waited to send them after, there's a charge per school.