@MadGamer76131 I've moved your post to the Sims 4 general discussion section, since it sounds like you're playing Sims 4. If you're playing a different Sims game, the principle below is the same; the difference is where your custom content needs to go.
You shouldn't be trying to open any custom content files that have a .package extension. Doing so is unnecessary and can damage the files. Just place them in your Mods folder, and they should work.
If you've downloaded .zip files, Windows and macOS should both open them without any help. For .rar and .7z files, you'd need a third-party app. 7-Zip and Unarchiver are both free and work well in Windows and macOS, respectively.
