Android Central has a great post on the basics of tethering for an Android phone. Link to PdaNet, video on WiFi tethering, and the pearl of info, using HTC Sync if your Android is using the Sense UI.

“If you have a phone running Android 2.1 with HTC Sense, mobile network sharing is built into the operating system.  Don’t get too excited though, because your carrier decides whether or not it will work.  If you want to try it for yourself, make sure you have the latest version of HTC Sync and plug your phone into your computer.  In the connection options, choose Internet sharing.”

Read on at Android Central …