You've probably heard about .zip files. They're computer files that are compressed, essentially just squished down in size, so they're easier to manage.
Google, for instance, compresses some of your photos on its free, cloud-based site, Google Photos. If you're receiving compressed files like .zip or .7z, perhaps in an email, you need a program to open them.
You may have heard of programs like WinRAR that do just that. (Note: WinRAR has had some issues with security, including earlier this fall.) Another program to open compressed files is Z-Opener.
Google's VirusTotal says Z-Opener is a clean site. But, make sure you have a rock-solid security software installed before you download any program.
Click on the blue link below, to start the Z-Opener download. Click on Free >> Open.
Once open, you'll see "Unpack File" If you're trying to open a compressed file on your computer, choose Desktop, then open the file.
If you want to compress a file, like a photo album, choose "Pack File." Find your file; highlight it, then hit Compress.