CE is best explained as a "demonstration" of Liferay. That said, it is relatively complete functionality but receives no support from Liferay at all. Bugs are reported and fixed, but releases of CE lag significantly. As many of these bugs represent security issues, I typically recommend using Liferay as an intranet solution, one which is not exposed on the internet. CE is open source, so your only real options are community support, but there is quite a bit of knowledge available in the forums, the wiki, as well as general blogs.
EE is the supported product. You get regular bug fixes and patches and is generally more secure and therefore more appropriate for internet usage. EE comes with a cost, however. I don't know the details of pricing, but I'm sure if you reach out to Liferay they will put you together with a sales representative. I would recommend that you have certain details available prior to talking with the sales rep including the number of servers that you'll be running Liferay on (if multiples), your expected number of users, as well as basic information about your business. Because it is a fully supported product, you get patches and support from Liferay itself.
Because of the cost involved, some folks elect to use CE as an internet solution. When choosing this route, you should always remember that you are really on your own for installation, development, support and maintenance.
