Summarize the following:
Finder is a blue icon with a smiling face at the bottom of your screen. It is located in the upper-right hand in Finder.  +Click on the file.  Normally, two files cannot share the same name. However, since your original Powerpoint file and new compressed file are two different types of files, they can share the same name.

Summary:
Click Finder. Click on the Search Bar. Type in the name of the PowerPoint file you want to zip. CTRL Click on "Compress [your_filename]". Enter a new name (optional). Press Return.