The MAPK cascade is comprised of three different steps. MAPKKK phosphorylates downstream MAPKK. In turn, MAPKK phosphorylates downstream MAPK. It is then MAPK that is the main signaler in the myriad different cellular functions.

This link is of a cartoon view of the MAPK pathway. It depicts original cellular uptake all the way through RNA Transcription.

http://www.biocreations.com/animations/_portfolio/MAPK.html