This is done by right clicking on the archive file and selecting the ‘Extract Here…’ option. You’ll want to use something like WINRAR to extract the mod files.
The download itself will be part of an archive file. Once you’ve confirmed your game version supports the mod, you can go ahead and download the mod files themselves. The first thing you’re going to need to do is make sure that your version of The Sims 4 supports the Wicked Whims mod.
Sims 4 WickedWhims: How to Download and Use Mods Downloading The Sims 4 Wicked Whims Check Your Game Version for Compatibility