You shouldn't need to find any cable for the drives, which is part of the reason to get the enclosure along with the replacement drive.
The internal drive uses the built-in connection, and the external drive enclosure would usually be USB, and comes with the cable
So, simple steps for replacing the drive.
Open MacBook
Remove old drive - install new drive in it's place (the new drive is connected internally, of course)
install old drive in the external enclosure. Connect cable from enclosure to your MacBoook, and that's your other cable. And, then you do whatever you need to do to transfer the old drive files and system to the new drive. Takes time, but it's all pretty simple.
There's nothing else that you need to install, no settings to change when you simply change out the memory sticks.
Another OWC video shows exactly how to open up your MacBook and change memory, but the hard drive swap, should you choose to do that, will get you inside, too - and the memory sticks will be right there, too.