Do I have a Virus?

So I was searching the web and I clicked on a link and then a window popped up telling me that a virus had infected my mac and that I should begin the repair process. Now, I'm new to MacBooks so I've never actually experienced this at all and I didn't know if it was legitimate or not. In a panic after it began repairing, I closed that tab and the whole 'repairer' thing went away and now I'm worried that I've let a virus infect my mac and I'm unsure on how to proceed any further. Many thanks.