mac book air

I have a mac book air and am still getting used to it. I recently downloaded an e-card from a friend and I think this is when the problem started. Now when I got to Safari search, it only comes up with the Yahoo search bar. Also, when I click on a link in an e-mail, it only comes up with the Yahoo search bar. I cannot get the link to come up. I tried clicking that Circle search button just to the left of the website address, and unchecked Yahoo as the default setting, but it didn't help. What can I do?