If you don’t want to create a designated swap partition (e.g. if you plan to downsize it later) and don’t want to play around with GPartEd, you can create a swapfile instead.

To create a 512 MiB swapfile, do the following:

dd if=/dev/zero of=/swapfile bs=1024K count=512
mkswap /swapfile
swapon /swapfile

To automatically add the swapfile upon boot, add this line to the /etc/fstab:

/swapfile     swap     swap     defaults     0    0

You can later easily change the size of the swapfile by re-creating a smaller or larger one.

You only have to make sure the file is contiguous or swapon might give an error.