Then create one
Use any partition utility. If you have to decrease any partition, save your important data of this partition on a different storage media first or at least on a different partition than the one you resize (but usually it is rather safe to decrease a partition size, if there is enough space left). Or you could also use a USB flash drive for swap (if you have more than you need). About 2 GB swap capacity should be enough, maybe even 1 GB.
Did you choose a manual partition setup during installation or was your configuration for partitions set automatically? I'm wondering why you don't have a swap partition.