Cordelia the answer is simple, read anything and everything you can put your hands on concerning Wicca. Surround yourself in its history, methods, and practice. There is no spell or ritual needed to start learning and practicing Wicca. In many physical Covens members will go through dedication and initiation rituals, which are particular to that group and practice.
On your own you can begin simply by learning on your own accord. Books by Raymond Buckland, Janet & Stewart Farrar, and Scott Cunningham can be excellent authors to get started with. All are well known in the Wiccan community. The list of "basics" that you will hear everyone repeat a little too often are another way to get started here on SOM.
Always remember to cross reference any information you stumble upon (meaning check it against various sources), question everything. Use your own common sense, chances are if it sounds far-fetched then it usually is. Other than that welcome to a new world, anytime you have questions we will all be right here. ;)