See this video for an excellent explanation of superantigens and the sequence of events they induce. A prototypical example of a superantigen is toxic shock syndrome toxin (TSST) released by S. aureus.
In a nutshell:
1) Superantigen binds periphery of T-cell and MHC molecule receptors
2) Non-selective T-cell activation with release of IFN-gamma
3) Macrophage activation and release of IL-1, IL-6 and TNF-alpha
4) Non-specific inflammatory response