There are a few different ways to tell if your file is a zip file by looking at it; you will see it says zip at the end of the file name, it will have a zipper on the file icon and for type it will say compressed (zipped) folder:
To extract the contents of the folder, double click to open; at the top banner, click to the right of the file on 'Compressed Folder Tools' and click on 'Extract all' directly below:
Select the destination of where you want to to save the extracted files by clicking browse:

If you have trouble located downloaded items, the easiest option is to download to your desktop
Select desktop to the left:
Right click within the window, click new and folder:
Title your folder and click 'Select Folder':
Confirm the destination and click Extract:
A status window will appear showing you zip file you are extracting from, the destination folder and the percentage complete:
Once the extraction is complete, the status window will disappear and your extracted files will show in the selected destination folder with thumbnails: