The introduction to wireshark is to introduce protocols, and lead people to the existing material and ask for more detailed desires.
Protocols 101 Wikipedia thinks it is long but not as long as college courses but it covers the basic level stuff but the article should open the rabbit hole a bit. http://en.wikipedia.org/wiki/Communications_protocol
A great Compendium of Protocols is here and very useful in under standing what wireshark shows you http://www.protocols.com/
To download for Windows or MAC use http://www.wireshark.org/download.html For Linux use a trusted Repository
Documents and training videos http://www.wireshark.org/docs/
The Wireshark Users Guide http://www.wireshark.org/docs/wsug_html_chunked/
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