To watch 3D videos on Youtube or Flickr you need a pair of special 3D glasses. Its lenses must be of two colors: red and cyan.

Usually the price for 3D glaases on eBay is around one dollar. However you can easily make them at home using a spare CD jewel case and some permanent marker pens.

Just scribble the transparent side of the jewel case with red and blue marker pens large enough to cover the width of your eyes. The blue (or cyan) color lens will be for the right eye while the red color will cover the left eye.

Alternatively, you may use a pair of sun-glasses that you already have and replace the lenses with colored pieces of transparent plastic. Or pick an old pair of eyeglasses and fill both the left and right lenses with red and blue permanent markers respectively.