How do I track seek in iPhone?

I got an iPhone 3G for Christmas. I am fairly tech-savvy but this is my first encounter with any smart phones or fancy mp3 players.

I can’t figure out how to track seek in a song or podcast, ie. fast forward, rewind, or jump to a specific point. It seems that the only thing I can do is to restart the track from the beginning.

Sorry if this has been asked before, but I just don’t have time to browse 5000 ipod topics, the majority of which are titled “help with ipod”. Thanks for your understanding.