You need a SATA enclosure,
https://www.newegg.com/Product/Prod...3.5+inch+hard+drive+enclosure&N=-1&isNodeId=1
Something like one of these, I didn't post a specific one because all of the ones I have tried worked fine... but I have heard some do not. So if I post a specific one and it doesn't work than that could be bad

They also change the electronics in these things all the time.
Basically some things to look for, make sure it has a power plug and USB 2/3 should work fine. Beyond that not much else to say. I would recommend formatting to NTFS unless you want to use GameCube games and some homebrew stuff uses Fat32. But if just Wii game loading is what you want, go with NTFS and enjoy
Edit: If you had the smaller 2.5 inch drive, you could get away with a USB powered enclosure. I use one of those on my Wii. Although if thumb drives keep getting cheaper and larger I can see myself eventually using one of those.