I find making a pinhole camera a bit difficult as blocking out all light from a box is a fiddle, nevertheless it is doable, simply find a box and using black ducktape block out all light that could get in, then make a small hole in one side of the box, then using a small bit of cardboard and a bit of tape create a flap over the hole that you can easily open and close.
Then pace a pice of photographic paper into the box opposite the hole you created in a darkroom of course. Next take the camera out and when you found a picture you want to take remove the tab for a short amount of time and close it again.
You can judge by the type of picture you get if you need to leave the tap open for longer or shorter time.
I found this video really useful for making the pinhole camera so check it out!