Sunnah and Hadith difference
Sunnah is anything that the Prophet (may Allah bestow peace and blessings upon him) continually performed within the following definitions. Hadith differs from Sunnah by the fact hadith can be correct, weak or fabricated (so on) but the Sunnah is what we know as the normalised practice.
Three types of Sunnah
One the Sunnah adheres one to the commands and avoidance of prohibitions and the Sunnah that is extra beautification of actions. The latter is more important but people place more importance to the former.
The second Sunnah, if performed is rewarded and not punished if not rewarded. Like standing under a tree and half of you is in the shade. Not following this Sunnah is not going to send you to hell but if its better if you do it. Do not misunderstand me if you are doing any Sunnah then keep doing it.
Three: Sunnahs we are not commanded to do and if we do them, we will be sinful. Marrying more than four women is haram, continually fasting without break and so forth. The Prophet (may Allah bestow peace and blessings upon him) was allowed by Allah (the Exalted) to have six wives but this is unlawful for anyone else. Continually fasting will harm to the body of most people.
There are things that the Prophet (may Allah bestow peace and blessings upon him) did that no one can do and these are known as Khasais/specific characteristics or actions.