Observing Jewish dietary laws means living within boundaries. Self-discipline is required, and each person or household has to decide how stringently to apply the rules--or what set of rules to follow. This often means adapting to the standards of the community in which you or your guests live.
Kashrut comes in several versions. Talmudic law was interpreted differently among medieval communities, leading to differences between Ashkenazic and Sephardic/Middle Eastern Jews on some of the fine points. Today, ideological and sociological distinctions are reflected in different standards of kashrut. Some keep "biblical kashrut," refraining from eating the meat of non-kosher animals but not separating milk from meat. Others are stringent at home but lenient in other settings.
Maintaining a stringently kosher home generally starts with making one's kitchen kosher--known as kashering it. One can "kasher" many implements used previously for non-kosher food. Kashering an entire kitchen may require many new purchases, but most metal items (pots and pans, silverware, even ovens and stoves) can be made kosher through heat--immersion in boiling water or blowtorching--while glassware may require only careful cleaning. Earthenware and stoneware cannot be kashered, but fine china may require little work to be usable. Some materials, such as Pyrex and plastics, are considered kasherable by some authorities and not others.
When shopping for packaged food, many people will only buy items marked with a symbol certifying it as kosher (known as a hekhsher). Each organization that grants certification has its own symbol, the most common in the U.S. being the Orthodox Union's "O" with a "U" inside. Some people will purchase items whose ingredients appear to be kosher, even without an indication of rabbinic supervision. Also, one has to know (or decide) which fresh foods, such as produce, do not require kashrut supervision and which do.