Good links to start experimenting with lenses in minimum expense
All below links will explain you how to build your own optical system in minimum expense and minimum effort without having theoretical knowledge of optics (Physics). It may be a good start to school students to wake up their interest in physics.
How to set up and focus Telescope – a beginner guide
How to turn a telescope into a microscope using a magnifying glass
Some easy ways to calculate focal length of a lens
Homemade cheap view finder for telescope