On most cameras, you can override the automatic ASA rating of the film (done by the DX code on the side of the canister). For 100 ASA, for example, pushing one stop means you manually set the ASA to 200. Pushing 2 stops would make you set it at 400.
After you've shot your film, tell the developer to develop it at +1 or +2 stops, as they must use different development times accordingly. This also means that if you want to push a film, you have to do the same for the entire film, not just a few frames.
Pushing any film one stop can usually be done with a minimum of loss of quality. 2 stops may be stretching it, depending on the film. Provia pushes quite well. I haven't tried Sensia.
The only thing you should feel when shooting a terrorist: Recoil.