Hey Jeanette,
Hope I can help.You push film to gain extra filmm speed,ie-setting your 100 sped film to 200,400,800,1600 in low light conditions(since your using a slow film this applies)pulling film reduces speed of film,ie-setting your ISO in you case to 50,25,etc in bright light conditions which your current film sped should be okay.when you push film you need toincrease dev. times by by 20percent for each one stop increase in exposure and conversely you decrease by 20 percentif you pulled your film.the best way to avoid having to increase or decrease dev. times is to bracket your exposures,ie-along with the meter reading go one above and under therebye making three exposures for each shot.in terms of making your ISO different than what its dx coded for(100 speed)
depending on your camera there should be an ISO marking on a dial somewhere andwhen turned on usually you cange it by turning the dial used for shutter speed but check your manual