A pretty general question... the best I can offer is that different people learn differently. For me, the best way to learn is to read a book on the topic and work with the products hands-on. If you want to learn about general networking, the best book is Radia Perlman's "Interconnections: Bridges, Routers, Switches and Internetworking Protocols." You can find it at http://www.amazon.com/exec/obidos/ASIN/0201634481/. Writing about a topic, or teaching someone else, are also excellent ways to become an expert.
This was first published in March 2001