There are three kinds of partition, primary, extended, and logical. What you need is either a primary or logical partition. Extended partitions are not usable on their own, but are really just containers for logical partitions.
A hard disk can only have up to four primary partitions. These will be named hda1-hda4 (or sda1, etc). If you need more than four, then you have to change one of those primaries to an extended partition, and then create one or more logical partitions inside of it. These extra partitions will be always be numbered from hda5 and up, no matter how many primaries you actually have. And of course the extended partition must be large enough to hold all of the logicals you plan to put in it.