You need to start the "Add/Remove Software" application

and then search for Etoys:

Click Apply, then it automatically notices the Squeak VM needs to be installed, too:

Click Install, then it installs both packages and offers to run them (choose Etoys, not Squeak):

This also lists the location where the menu item for launching Etoys later is located. Currently it is slightly miscategorized:

Currently this does not properly set up the browser plugin. A workaround is to type the following commands in a Terminal:
su
/usr/share/squeak/npsqueakregister
ln -s /usr/share/etoys/etoys.image /usr/lib/squeak/SqueakPlugin.image
