For games like Guitar Freaks and the newer Guitar Hero, the controller is in the shape of a guitar, complete with buttons on the neck and a strum bar.
Complete with a strum bar, whammy bar, and five different colored buttons on the neck.The strum bar is a little plastic flipper that clicks up or down, simulating the strumming motion you would make when plucking strings.
You'll notice you're given no indication of how to sing the lyrics or how to strum the chords, so you will either need to know the song very well or have a recording of it handy so you can get the rhythm right.
As colored icons come down the note "highway" on the game's screen, the player must then hold the appropriately colored fret button(s) down and hit the strum bar in time with the music.
Although taking these lessons online offers many benefits, it might still be a good idea to take a lesson or two in person to learn the basics of how to hold a guitar and how to strum.