The exact method you use to create the partitions is interface-dependent, but Linux tries to use any partitioning scheme that is already present. The appendix asks you to type 'Y'. You want to answer 'N' here. HForm will ask you for the make of the hard drive. You should accept the values HForm suggests for sectors per track and heads.
Guidance is given below.
Accept all the defaults for any other options that HForm asks. Continue with the procedure in the appendix. You can define many partitions of any size. Generally the idea is to create space towards the end of the disk, and if the software for the interface allows it, to use this software to create the partitions. The following table suggests partition sizes.