1. Symposium: A 'super-conference' of smaller conferences, e.g.: http://www.ieee-ssci.org/
a. a meeting or conference for the public discussion of some topic especially one in which the participants form an audience and make presentations
2. Conference: e.g. http://www.computelligence.org/sis/2007/
a. one of the conferences as part of the symposium, above.
b. Conferences are occasional or annual meetings organized by a committee, with a group of appointed paper reviewers who review submissions and select the most suitable, original, best etc. papers for publication in a book: 'conference proceedings'.
c. Conferences are self-funded - i.e. people attend because they are interested in the conference subject matter. People who attend pay a registration fee, which provides for e.g. a printed book of proceedings for all registrants.
a. There are nominal differences between a workshop and a conference paper
b. A workshop paper isn't technically a publication and is typically meant to represent work-in-progress
c. Nowadays, workshops are typically very topically-focused and non necessarily any less quality than a conference paper
d. That being said, I think it’s safe to say workshop papers are generally regarded as less prestigious than conference papers.
4. Journal: e.g. one of Nature's publications, http://www.nature.com/ng/index.html
a. Journals are usually peer-reviewed, which means your paper was carefully evaluated for errors and possibly rewritten a few times. It also could have been rejected. Conference papers (or proceedings) take whatever you send them if you participated in the conference. Journal articles (from peer-reviewed journals) are better.