For this simple and fully-functioning Pan Flute, you will need a pair of scissors, tape (any tape will do, as long as it's strong enough to hold the instrument together), and at least 10 straws (in the example, I've used 6).
To get the different notes, you will first need to cut each straw down, each one smaller than the last until you get to your stopping point.
Then, you will need to arrange your straws from the biggest to smallest; make sure that the end you're blowing into are approximately leveled.
Once you're sure you have your straws aligned as you like, you can begin laying them down on a bed of your tape, then cover them with another strip of tape. You will need to make sure that, if you leave a gap between the straws like I did, that you press the tape through the gaps.
Then there you have it, a fun and easy little pan flute to play to your heart's content!