To be honest most people will leave their drives as one partion when running OSX, however if you prefer to partition your drives into two or more drives than all you will need to do is open Applications then utilities and then choose the disk utility application.
Once it opens can you then select your drive on the left and choose partition.
When the window opens can you then choose your existing partition in the list and then click Add.
Disk Utility will then split the partition into two leaving the data in one of the new partitions.
Atthis point you can resize the partitions as needed, To do this you can drag the dividers between the partitions in the Volume list till you get the size you wish.
Then all you need to do is to choose how to format the partitions that will be erased or created.?For each new partition all you do is select it then enter a name and then choose a format and just hit apply.
If you would try that then let us know if you need any more information or clarification.
To be honest I use the same partition on all my OSX machines as OSX uses any spare hard drive space as what is known as a swap file so having all the spare space on one partition tends to make the machine faster.
The only time I will run partitions or seperate drives is on an OSX server installation when I need to control access to the files and drives.
Personally I would keep it all on one partition unless you have a huge hard drive or just have to have the extra level of security when sharing files and folders.
Can you tell me if you are just doing this for performance or for some other reason?
In that case you may wish to split the drive into 2 or 3 partitions if you wish.
If you would like to then I would suggest a 100GB OS drive for software and the OS then 1 400GB or 2 200GB drives to store data, However the performance gains will not be that big so it is entirely up to you.
If you would like to do this you can always use the partition application to delete the additional partitions later and recombine it all into one if you dont like the result.
It is usually best before you start using it, However if you dont it will not hurt.