Sunni sects are four:
1. Hanafi Sunnis who follow Abu Hanifa Ibn No'maan who was born on year 80 after Hijra, after 70 years of the passing away of the Prophet Muhammad (SAWA) and died on 150 after Hijra.
2. Shafi'ee Sunnis who follow Mohammad Ibn Edrees al-Shafi'ee who was born on year 150 after Hijra and passed away on 204 after Hijra.
3. Maliki Sunnis who follow Malik Ibn Anas who was born in 93 Hijri and passed away on 179 Hijri in Madinah.
4. Hanbali Sunnis who follow Ahmad Ibn Hanbal who was born in 164 Hijri and passed away on 241 Hijri.
Shia follow Ahlul Bayt who are Imam Ali, Fatimah, Imam Hasan, Imam Husain who lived with the Prophet Muhammad (SAWA). Then the 9 Imams from the kinship of Imam Husain (AS).
Shia is not a sect but a title which is used in Quran for the sincere followers ( Sura Al-Saffaat 83 and Sura Al-Qassas 15). The Prophet Muhammad (SAWA) gave the title of Shia of Ali to the most pious of his companion and most obedient Muslims ( Tafseer Al-Tabari, V.30, P. 335) and Shawaahid al-Tanzeel by al-Hasakaani 2: 353 and Tafseer al-Dorr al- Manthour by Al-Soyouti 6:379.
Shia believe and follow the Prophetic order to all Muslims to keep following Quran and Ahlul Bayt (AS) to be andbremain on the Right Path. This Hadeeth is authentic and narrated in Saheeh Muslim 4425, and Tirmithi 3718 and 3720 and in many authentic Sunni books.
Shia follows the Prophetic Hadeeth that the successors of the Prophet will be twelve. (Saheeh al-Bukhari 6682, al-Tareekh al-Kabeer by Al-Bukhari 8:410), Saheeh Muslim 3393, 3394, 3395, 3396 and many other important Sunni books.
Shia believe that the Prophet Muhammad (SAWA) `did not leave the Muslim Ummah unguided regarding the divine leaders of Muslims after him, but he clearly informed the Ummah and asked them to give allegiance to Imam Ali (AS) being the first successor of the Prophet Muhammad (SAWA).
Shia Muslims follow the Prophetic Sunnah of the Prophet which is Been narrated by the most authentic source who are Ahlul Bayt (AS) and their pious followers.
The main difference between Shia and Sunni Muslims are in two issues: First : Who succeeds the Prophet in leading and guiding the Muslim Ummah?
Second: From where we should get the prophetic teachings ( Sunnah and Quranic meanings) after the Prophet Muhammad (SAWA).
Most of the tyrant governments like Bani Omayyah and Bani Abbas till today are against Shia Islam and played big role in defaming Shia Islam and spreading false propaganda against Shia.
Shia Muslims present evidence that they are following the original teachings of the Prophet (SAWA) not only from their books but also from the Sunni books and always call and practice dialogue.
You can find more details on this subject in many books written by ex Sunni scholars who reached to the reality of Shia Islam through scientific research like books of Dr Tijani and other scholars which can be seen in www.aqaid.com and www.al-Islam.org and many other websites.