Partitions are very important, they divide your hard drive into different parts (drives), which may make certain things easier. A little history first - in my experience with Windows, I always have a C: for my Windows installation and Program Files, while D: is for My Documents. In Peppermint, they are / and /home.
I asked the helpful Peppermint Community: http://forum.peppermintos.com/index.php?topic=772.msg6547#msg6547 and a very helpful user game me a link. Which was trustworthy and worked.
I now have 20 GB for /, a little for SWAP and the rest of my 160 GB HDD goes to /home.