The rules for Kosher are strange, archaic and confusing. Many people opt to just get prepared foods that have been certified. But I actually find that the easiest thing to do is just learn the simple rules for whole ingredients and prepare meals yourself. There is no such thing as kosher for passover broccoli, it is and has always been kosher (despite what some young Jewish boys might claim).
And one must understand the rules for Kosher vary. The Ashkenazic rules that @Thas talks about are one major set of rules (and they are themselves conflicted) and then there Sephardic rules. I am reform and take a very liberal stance towards Kosher rules. And I also recognize that for the sick or infirm (like someone with diabetes) there has always been a dispensation from the strict adherence to rules about fasting and diet. I work to enjoy Passover, make a couple extra briskets and eat them all week.