Captain Picard giving Devor a Vulcan nerve pinch, causing him to experience pain
Garak collapses in pain
Pain was a feeling felt by most humanoids which was caused by intense or damaging stimuli, like stubbing a toe, being struck by a phaser, being punched, etc. Pain could also be emotional, like pain caused by grief or remorse.
During his interrogation of Captain Jonathan Archer in June 2151, the Andorian Commander Thy'lek Shran suggested that Archer must enjoy pain. (ENT: "The Andorian Incident")
In 2152, Doctor Phlox's treatment of Malcolm Reed's impaled foot caused him great pain. Reed stated that it could not be ethical, but Phlox replied that while it was unethical to harm a patient, he could inflict as much pain as he liked. (ENT: "Dead Stop")
One of the symptoms of the life prolongation project virus was great pain in the extremities. (TOS: "Miri")
Victims of Kodos the Executioner's massacre of 2246 died quickly without pain. (TOS: "The Conscience of the King")
In 2287, Leonard McCoy claimed that Sybok took away his pain, but James T. Kirk noted that as McCoy was a doctor, he knew that pain and guilt couldn't be taken away with the wave of a magic wand. They were things people carried with them; what made them who they were. If they lost them, they lost themselves. Kirk didn't want his pain taken away because he needed it. (Star Trek V: The Final Frontier)
For most Betazoids born with their telepathic abilities switched on, the noise of other peoples' thoughts and feelings were overwhelming, incomprehensible, and painful, especially to a child. (TNG: "Tin Man")
The Vulcan nerve pinch was a pain-inducing technique most commonly carried out by Vulcans or the select few who had mastered it. (TNG: "Starship Mine")
One of the symptoms of the phage was excruciating joint pain, so much so that some patients died from the pain alone. (VOY: "Faces")
The Emergency Medical Holographic program was not programmed to feel pain. As such, The Doctor was confused when he experienced it during a hallucination in 2371 in which he was not sure whether he was actually an EMH or the Human named Lewis Zimmerman. (VOY: "Projections") In 2373, when The Doctor's program was captured by Henry Starling, Starling demanded Captain Kathryn Janeway's psychological profile. The Doctor refused, countering that Starling had no means of coercing him, and Starling tapped a button, proving that he had reprogrammed him to feel pain, then further tortured him with a burning sensation. (VOY: "Future's End, Part II")
Vulcans were capable of suppressing certain levels of physical pain. Beyond this, they had no choice but to endure it. (VOY: "Resistance")