Hello. For all those to whom the concepts of general relativity, big bang and universal expansion are not clear, I just updated my page of cosmology. There I presented a rather simple proof of the Friedmann equations, that are the particular case of the Einstein's equation of General Relativity for cosmology, but without assuming its prior knowledge by the reader. I do it through some simple descriptions of curved geometry and simple differential equations (with just one variable: time), without any explicit use of the tensor formalism. This presentation can be used as an introduction to General Relativity, as it explains the relation between the simplest (diagonal) components of matter (energy and pressure) and space-time curvature, that can suffice for some simple cases, without the full mathematical formalism that would be needed for more complex situations.