You can't 'make' the special resources exactly. They are put on the map in a certain pattern. You can then build a city on or near them to be able to use them. Say you have a city next to a special resource, to use it you click on your city, then look in the upper left corner of that screen. It will show you your city in the middle and the terrain around it. One of the squares will have some icons on it (this is one of your citizens working the land) click on that square to remove the worker. Click another square to put the worker there.
The Silk resource actually increases trade for the square, not food. You can see this by putting one of you workers from the city screen on a plain forest sqaure. Then move that same worker to the silk square and you will see the extra icons that are there from the 'special' resource.
The civlopedia just shows you that the special resources are availbe on certain types of terrian. The game uses a pattern to put out the speical resources (as well as the huts), so depending on the terrain type that is in the given square, you will get a 'special' resource.
P.S. You can 'make' speical resources in one way. The only usable terrain to not get specials is grasslands. So once you recognize the pattern, you can actually mine the square to turn it into a forest and 'make' a speical resource appear.
