Describers are basically adjectives—cold, blue, light, steady—used to the describe qualities of the noun.
Intensifiers are usually adverbs, words like very, extremely, really—or, conversely, words such as slightly, fairly, a little—all of which modulate the intensity of a describer.
For more detail on describers and intensifiers, see the lessons on adjective groups and adverb groups.
Note that noun groups can have these other word groups embedded inside them—this concept will come up a lot in the other word group lessons.