WHAT ARE SUNNIS?
"Sunni" is a word used in reference the Arabic term "Sunnah" which means to follow or to go by the words and actions or the example of the Islamic Prohet Mohamed SAW in terms of religious practice and daily life.
[If this post is AT ALL sounding biased, remember, I am most likely to be labelled a Sunni, being the majority of my beliefs and practices are in tune with Sunni Islam]
WHERE DID THE SUNNIS COME FROM?
The Sunnis came from the first generation of Muslims who followed the Islamic Prophet Mohamed SAW.
All Muslims began in this group, as all Muslims in the world likely claim to follow the sunnah of the Prophet Mohamed SAW, even those who are not Sunni, like the Ibadhi and the Shia.
The Sunnis of these days are specifically those who, at the time of the death of the Prophet Mohamed SAW, chose to follow the man who the Prophet himself said was most qualified to lead the Muslims in his absence, Abu Bakr (the first male convert to Islam) over Ali, the Prophet's son-in-law (also, arguably, highly qualified to do so).
WHAT DO THE SUNNIS BELIEVE?
Those who are Sunni believe in following the words and example of the Prophet Mohamed SAW in all religious and daily affairs. Individual followers have the same basic belief system but differ from one another in terms of practice and execution of rituals, and in juristic interpretation of "divine principles" (or Shariah) as envisaged in Quran and Hadith. However Sunni Muslims consider them all equally valid if their core beliefs are the oneness of Allah, and dependence on the Quran and the Prophet Mohamed for directives, rather than those around him or anyone who made a new directive after him.
And while there is a consensus is that Shari'ah [the definition of the religion by its doctrines and laws] does not change from the directives and examples of the Prophet Mohamed SAW himself, its jurisprudence rulings [fiqh] change all the time to include, for example, whether or not downloading pirated software is sinful, basing all .
Additionally, and most importantly to the evolution of different idealogies in Islam, at the time of the death of the Prophet Mohamed, Sunnis believed Abu Bakr was chosen to lead the Muslim nation because he had been chosen to lead the Muslims by the Prophet Mohamed during his illness before his death. They believe Abu Bakr was chosen because of his merits and capabilities, rather than his relation to the Prophet's household through marriage contracts. This is the same as Ibadhi believe but different than what shia believe.
They also believe strongly in the mercy of God, and only believe that those who die disbelieving in God, will dwell eternally in hell.
On history and the Islamic Caliphate/Leadership of the Muslim Population: The Sunni branch accepts the first four caliphs as rightful successors of Muhammad.
[Which I am still on the fence with, personally....... though I still consider myself Sunni]
Veiw of hadith:
Most Sunni Muslims accept the complilations of ahadith by 1.Bukhari and 2.Muslim as the most reliable and correct, while accepting all hadiths that are verified as authentic, such as hadiths in the compilations of 3. Sunan an-Nasa'ii, 4. Sunan Abu Dawud, 5. Sunan at-Tirmidhi, 6. Sunan ibn Majah, 7. Muwatta of Imam Malik, 8. Musnad of Ahmad ibn Hanbal, 9. Sahih Ibn Khuzaymah, 10. Sahih Ibn Hibbaan, 11. Mustadrak of Al Haakim, and 12. Musannaf of Abd al-Razzaq.
[I am agreed]