Extinguishing a candle is a melocho on Shabbos. But putting it out for a reason besides making the candle itself better would be a מלאכה שאינה צריכה לגופה- that’s a dispute between r yehuda (obligated) and r shimon (exempt). Examples would be to save oil, lamp, or save a wick, so someone could fall asleep better, etc.

Everyone agrees it is permissible to put out a candle for a life threatening scenario.

There are pesukim in both Koheles and mishlei that seemingly contradict each other and contradict points from tehillim, and bc of this, the rabbis did not want to have these seforim in tanach, but ultimately, answers are provided and they are included

Only live people can do torah or mitzvos. Dead people’s merit is greater than live people. Also, decrees from the dead (like moshe rabeinu) cns be greater than decrees of living Kings. When shlomo tried bringing in the Aron to the Kodeh Kodshim, rhe gates refused to open until he invoked the merit of his dead father, Dovid. This was the sign Dovid was forgiven for his sin with Batsheva.

Dovid died on a Shabbos when he stopped learning for one second. His body was muktzeh and it was moved only indirectly together with other non muktzeh items.

Laughter is described in Koheles as good and bad. It’s bad referring to laughter with the wicked that is jsut to give them reward in their word. It’s good for the righteous in the World to Come.

Happiness is also described as good and bad. It’s only good when it’s associated with a mitzvah. Happiness is a tool for prophecy and for learning Halacha.

A teacher should start torah lesson with a joke. Students should always be serious.

For most matters, we don’t respond to a fool. But in torah, we respond and answer a fools claims