When you partition you lose all of your data unless you use a tool like partition magic (but even then it is a good idea to backup stuff that you don't want lost forever). Fdisk works fine for partitioning but some users find it hard to use--it is pretty intuitive, just play artound a bit to get the feel for it. Fdisk will not preserve data in any way, so when it writes the new partition table to the disk, all the info is gone.
Ideally, you'll want the following partitions for each Linux install:
/swap (2X RAM or 700MB, whichever is smaller)
/ (2GB-10GB for OS and applications)
/home (the rest)
It can also be a good idea to set /tmp and /boot to seperate partitions as well, but if you are just playing around, you'll be fine without doing that.