1 What, exactly, was it that you just bought? I don't know what a "loop library" is.

2 They're content libraries for making music.  Rather than just having a synthesized piano sound, or a set of recorded piano notes, loops are live recordings of musicians cut into little pieces (typically 1, 2, or 4 bars) and timed and edited so that they repeat perfectly.

Plus each file is tagged with its key and tempo, and the software can shift the pitch and tempo to match that of the song.  Though that's not perfect with the software I have; sometimes it works great, but sometimes you can tell.  I try to use loops that match the key I'm working in and are pretty close to the tempo so there's minimal change.

So rather than having to sequence everything using a MIDI keyboard or a software sequencer, you can string together these pieces of rhythm and melody to produce music, so that even if you're a no-good talentless like me you can do stuff like this or this.

3 That is, the recordings are cut into little pieces.  Musicians tend to give unsatisfactory performances when diced.

4 Thank you.

5 Musical clip-art.