On emac-can not read(open) my down load(on the big blue screen)?

(eMAC, safari, yahoo) I download the attachment, but I can not read/open it - I see a square like picture with "cpgz" on it or "ZIp" - both have zippers in the squares. I have no idea what is going on or how to read the attachment or what caused it. Yes, I am computer ignorant. Friendly help would be appreciated.