how to get rid of malware on macbook air piet e

how to get rid of malware on macbook air

it loads up a new browser page but then quickly keeps changing the addy in the addy bar at the top.

sometimes it's piet 2exix, or piet pixel zrryz1.. all because I opened an email that in hindsight I should not have opened!!

Please tell me how to find it in my MacBook air and how to get rid of it?

thanks

maddy