Becoming an Academy Student is the first step to becoming a professional ninja. Students are taught the basics to become a ninja. Rather than performing missions, all students are trained to master basic techniques and skills. All students enrolled are of very young age. In order to become a Genin, students must pass a comprehensive graduating test. Passing this test gives you all the chance in the world to become a great ninja. It is not very easy to make the cut and many students don't pass. Passing this rank is probably he most crucial stage towards becoming an elite ninja.
Genin 
The Genin is considered the lowest rank for a ninja. Most Genins don't perform missions, but train like academy students. Genin ranked ninjas usually perform harsh labor and dirty work. When put into missions, they usually perform D ranked missions. Every Genin is assigned a Jounin instructor. The Jounin instructor helps train the Genin to become a wise and skilled ninja.
Chuunin
Chuunin rank is a medium ninja rank but hard to attain; the exams happen twice a year. A Genin team must be nominated by their Sensei and endure grueling written, physical, and mental exams to prove that he or she has what it takes to be a Chuunin. Ninjas have been killed during the Chuunin finals. When Naruto's team takes the Chuunin exam, only one person attains this title (Shikamaru). A Chuunin is considered a leader and is responsible for those under his command. Their mission parameters broaden and include higher-level missions ranging from simple escort or intelligence gathering to open combat and even assination.
Jounin
The title Jounin is split into two separate categories. Before you are awarded the full title Jounin, you are, by appointment, a Special Jounin. This is the next rank up from Chuunin and covers everything a Chuunin does, but also includes high-risk missions between other countries, such as: escorting royalty. These missions are much more delicate and dangerous than previous missions. Complete Jounins are assigned to the most dangerous and highest paying missions. These missions can be anything from high-level inter-nation assassinations to delivering and collecting important documents and treaties. Only a ninja with a wealth of combat experience can become a full Jounin. At some point in a Jounin's career he or she will be assigned a team of Genin to teach and guide their development. This responsibility is huge as they will oversee their students training and be responsible for their lives until they are Chuunin.
ANBU
The ANBU is not exactly a rank of a ninja. The ANBU operates as top-level assassins, interrogators, and also hunters of ninja who, for whatever reason, have defected from their village. They are a secretive organization that exists in every village and are under the direct orders of their Kage. Life expectancy for ANBU members is very short as they have the most dangerous assignments; they wear animal masks (representing the animals of the Zodiac) to protect their identity and to further induce fear into their targets. ANBU members also have a tattoo on their shoulder.
Sannin
Sannins are ninjas with with immense skill. Many times they are as powerful, if not more powerful, than Kages. They usually live away from the village to keep a low profile but are forced to keep in touch with the village every now and then for safety measures. Orochimaru, Jiraiya, and Tsunade are all considered to be Sannins
Kage
The Kage is the hidden village's respective leader. Kages are ninjas that are among the strongest, if not the strongest ninja in their village. In order to become a Kage, they have to climb the proverbial "ladder" from the Genin rank. Kages are responsible for the protection and well being of their people and all the important the decision making falls on their shoulders. There is a council of elders that they often consult for high-level decisions, but ultimately, the Kage has the final say. A new Kage is hand picked and groomed by the current Kage to take their place.
