How do you unzip a file?

I copied some pictures from my digital camera and when I attached them to an email to my husband they can be opened one at a time, but the whole file is zipped and if you try to open the group the computer starts flashing and the only way to stop it is to close down the computer it and restart it.

Is there any way to unzip the file? I didn't re-size the pictures because he wants to use them in a PowerPoint presentation and I was afraid it would affect the quality. I can load thes pictures directly into his computer, but I want to know what I did wrong so I don't have this problem when I email pictures to other people in the future.

I have emailed pictures in the past and this is the first time this has happened. I would appreciate your help with this problem.