How is fire made through a magnifying glass?

Answer 1

material can absorb or reflect photons.
if you go out into the sun with a black t-shirt you feel the shirt heat up in the sunlight cause photons get absorbed by the material. This is an energy transfer. The absorption transfers energy into your shirt, which as a result heats up

using a magnifying glass on a surface means focussing a stream of photons on a small area which absorbs much more photons like that, and therefor heats up much more.

if you use a material which cannot lead, radiate or reflect the heat away it heats up above igniton temperature

Answer 2

The light rays from the sun are concentrated to a small point. This point gets hot enough to set paper on fire.

Answer 3

It just concentrates the Suns energy to a focused point, and it gets hot enough to burn stuff