The sol-gel transition (also known as gelation) is simply a change from a liquid state to a gel state. In the liquid state, components dispersed in the liquid are relatively free to move about. In the gel state, these sub-units bond together to form a network extending throughout the whole substance (see figure 1). This network gives the material an elasticity: a solid-like property [1, p. 95].
The composition of the sub-units and the bonds between them play an important role in the properties of the gel. [1, p. 95].
You can witness the sol-gel transition by curing epoxy , making a dessert with gelatin, or making Jam with pectin.
For more on gelatin: http://www.gelatin.co.za/gltn1.html
For more on Jam and the pectin which make's it undergo a sol-gel transition: http://www.gi.alaska.edu/ScienceForum/ASF8/887.html http://www1.lsbu.ac.uk/water/hypec.html#fun
 R. Jones, "Soft Condensed Matter," Oxford University Press Inc., New York (2002).