Partition Magic is relatively straightforward to use
Which version do you have?
When you use it, and you want another partition, you simply click on the 'create partition' bit, and follow the questions. You don't want to make the partition a bootable one, you want to make it FAT32, and you should generally pick a partition to follow (the recommended option). You then have to decide upon the size of partition you want. It will give you a size generally half of the size of the space available. You can change this by typing in the size in Mb ie. 3gig is 3000 in the box
Now this is where the previous advice comes into play.
I recommend that you have the OS and all programs in one partition.... the reason for this is that if you have to reinstall your operating system, you will have to reinstall all your programs too. So it makes sense to wipe them all from your HD and start with a nice clean surface, without any remenant files.
This means your partition can be used purely for data etc, It does however mean you need to be careful when using applications to ensure you redirect the saved files to this new partition and not just rely upon the default locations.
If you need more assistance, just ask