What does it mean when one is feeling pain when excreting or releasing stool which also comes out very small?

Anal fissure?: It would require an examination, however, what you described suggests an anal fissure and it would be prudent to see your doctor for an evaluation and treatment.

Rectal pain: Rectal pain could be due to hemorrhoids, an anal fissure, inflammation of the rectum (proctitis), inflammation of the colon (colitis) or, more rarely, a tumor or abscess. It merits a visit to your doctor.

Constipation: You may be having some constipation. Try taking a mild laxative like miralax, (polyethylene glycol) drinking extra water, and increasing your daily dietary fiber.