Need help with zip/compression software

So recently I wanted to change my windows 7 theme, rainmeter skin, and other skins. I've found a bunch of great skins but they're in zip files, and I have no clue on how to uncompress those files.

I actually got my windows 7 theme to work 100% by clicking "stuff" but I don't have the slightest clue on how I did it.

I've looked for guides but they're all too brief or outdated. Could you guys recommend me a good, free unzipping program? Which one should I use? Winzip? Winrar? 7 zip? I know that some of them are only trial programs. If I could get a forever-free program that would be nice. I'm only a common consumer so all I need is an easy unzipping tool.

And, could you guys explain to me how to use the software? Could you guys explain the terms such as "extract, archive, zip to folder, etc"?

For example, I want to install a Rainmeter skin.
After downloading the zip file, I use a zip program and open it. Then I see a bunch of folders in that file. Which one do I use? Do I copy/paste the entire folder into the rainmeter skin folder? Or do I open each zip folder and find the specific skin?

Sorry, this might be confusing but if somebody could help that would be nice.
I've tried to find guides on youtube but many of them skip the zip/unzipping process.

 

7-Zip totally free forever. download which ever os you have and install.

you can either double click to open the zip file or right-click drag to extract where ever you want.

As for the skins, they all can be different to install in my experience so best thing to do is to check google for installation instructions.