Texworks is a TeX editor, not a TeX distribution (as far as I know). The way to manage packages will depend on which TeX distribution you are using / how you installed TeX. The most common are installing TeX Live either through Ubuntu's package manager (
apt-get or a GUI version of it) or manually (
If you installed TeX through Ubuntu's package manager, everything will be handled through it too. Look for packages called
texlive-..., i.e., to install
pstricks, use the command
apt-get install texlive-pstricks
This way of installing teX on Ubuntu is common as it easy, but the drawback is that packages can be (significantly) outdated, as updates are infrequent.
Installing TeXLive directly (called a "vanilla" installation) is a little more hassle, but you get the benefits of an up-to-date installation.
There is already a howto on TeX.sx on how to perform such an installation: How to install "vanilla" TeXLive on Debian or Ubuntu?
As for how to manage packages, you will then be using a tool called
tlmgr. The full documentation is available online, and the short answer is that you install packages with
tlmgr install <package name>
and update the whole system with
tlmgr update -all