Acoustic guitars work a lot like electric guitars and basses(see previous blog posts). They have six strings. The note the string plays depends on the frequency. The frequency depends on the length, mass and tension of the string. So that means that you'll have to tune and string your guitar differently depending on what strings you use.
When you play a note, the strings vibrate and produce a sound. The note produced depends on the frequency. This is pretty much universal in all string instruments. You can alter this by changing the length, so pressing down on the frets, the tension, use the tuning pegs, or the mass, by using a completely different string. I would recommend the first two options and not going to but a new string every time you tune your guitar.
However, the acoustic guitar has something that an electric guitar doesn't and that's a vibrating top plate. the vibrating top plate creates an air cavity resonance that will amplify the sound of the strings. the vibration of the strings gets to the bridge and the vibration of the bridge is what causes the top plate to vibrate.
The air cavity resonance can be affected by a lot of factors including the type of wood, as well as the size of the body and the hole. Antonio de Torres Jurado created a style of strutting that has the struts diverge from the sound hole on the top plate, creating a more sustained tone.