Sharan STD-35 Pinhole Camera Kit on Amazon.
Sharan SQ-35 Square Format Pinhole Camera Kit on Amazon.
Sharan SW-35 Panoramic Pinhole Camera Kit on Amazon.
Remember kids, this is a film project so you might not get the best pictures right away. My suggestion is to shoot a test roll of film... ok hold on, I have a list of steps.
Step 1: on a normalish/bright day go out with your camera and place it somewhere steady making sure there's something in the foreground, mid and background for comparison later.
Step B: keeping an eye on the time, expose your very first photo for 1 second. Then take your second shot for 2 seconds then 4 then 6 then 8 and so on until you reach 30 seconds without ever moving the camera. Use the rest of your roll of film to experiment with different times, double exposures, movement - all that arty shit you wanted to do with it in the first place. You just bought AND built a cardboard camera remember?! XD
Step III: after you develop the film your first 15 shots will serve as a visual guide of what exposure time you should use on a regular day and what effects the different times give you. You'll be able to shoot relatively freely afterwards and if it's a cloudy day just double the time or eye ball it. As you shoot more you'll hone that.
Note: If you have very bright streaks of light ruining your photos then there's a light leak in the camera. Buy that cloth-like black tape and tape up the seams. That should help. If the light leaks are slight it could be stylish but if it's ruining everything then you should totes tape it. Also, there's some great notes at the Sharan website about exposure times with photo examples here.