Study French. Most legal education in France is based on the native language. The few programs that offer an English option are usually taught in both French and English and will require a high level of fluency in both languages.
Choose a program for your "license," which is roughly the equivalent of an American Bachelor's degree. The Campus France website, sponsored by the French government, can help you narrow down your options for the license and subsequent degrees you will need.
In France, law schools are part of larger universities. Unlike in the U.S., students usually go to law school right after high school and spend their first three years studying for their "license." Keep in mind that law schools may focus on the laws of their particular region in France.
Enroll in a Master of Law program. This Master's degree will take two years to complete, and specializes in a particular kind of law (public, private, international, etc.). Students normally do an internship or research during the second year.
Enroll in a specific program to study for the bar. These programs (at institutions called the Centres Régionals de Formation Professionnelle d'Avocat, or CRFPA) are open to students who have finished the first year of their Master's degree. These programs usually last about a year and a half.
Take the exam to become a licensed lawyer (Certificat d'Aptitude à la Profession d'Avocat, or CAPA). Administrators at the CRFPA you attend can help you organize your registration and attendance at this exam.