Tape media are the actual removable tape cartridges that hold the data, tape drives are the machines that write the data to the cartridges and tape libraries/auto-loaders are one or more tape drives that are capable of managing multiple tape cartridges. You'd definitely going to need either a library or auto-loader for the amount of data you need to store.
If you can you need to go for the most capacitous tape cartridges you can (currently LTO-7 if I recall correctly) as they're comparatively fast and hold the most data - you'll need less of them that way you see.
What I would say is that you need help, I'm not being nasty but if you needed help with the basic terms there's a pretty good chance you'll need help spec'ing and implementing a system such as this. Now Dell don't actually make those items, they re-badge them, if I were you I'd contact Quantum who probably make that kit originally and get them to help you directly, they've always been very helpful for me in the past anyway. You'll also need to pick some form of backup software to drive the tape system - most OS's come with enough to fire them up but they lack a lot of very useful features - look at NetBackup or my favourite Commvault Simpana - these will do a great job of backing up and managing your whole data requirements via a GUI.