There are a few different connections to worry about. The main one is going to be either an 80-wire or 40-wire IDE/ATA (sometimes called PATA) cable. The one pictured here (it’s large and yellow) is a 40-wire. It will be obvious where it goes in the back of the hard drive. Some drives will have 80-wire connections, others 40-wire connections, and still others will have both. Make sure that both your enclosure and your internal drive have a matching connectivity.
There are also a few other scenarios you’ll come across. A SATA connection can be used to connect certain newer hard drives to an enclosure, or inside your PC. What connection it uses is irrelevant, however, what remains important is that you know what your hard drive connects with, and that you buy an enclosure capable of accommodating that connection.
The other connections are even more straightforward. They each serve their purpose, but the main thing you need to know is that there will only be one place to plug them in. Match them up and slide them in, and you’re all connected.