Plug the USB into the PS4. Go to Settings > Devices > USB Storage Devices to ensure it is recognized.
For most users, the phrase "Save Game PS4 Download" implies recovering their own progress. The easiest way to do this is via PlayStation Plus. Save Game Ps4 Download
If you subscribe to PlayStation Plus, Sony automatically uploads your saves to the cloud. Here’s how to manually download them: Plug the USB into the PS4
Enable auto-upload in Settings > Power Save Settings > Set Features Available in Rest Mode to ensure your saves are always backed up overnight. The easiest way to do this is via PlayStation Plus
However, due to Sony's encryption, you cannot simply drag and drop a stranger's save file onto your PS4 and have it work. The file is encrypted to the original owner's PSN ID.
PlayStation 4 saves are , meaning you cannot simply copy a file from the internet and play it on your profile. To make a foreign save work, you generally need specialized tools to "re-sign" the file to your unique Account ID: Apollo Save Tool Full Guide for Jailbroken PS4