Urinary catheterization is a medical procedure that involves inserting a catheter into the bladder via the urethra for therapeutic or diagnostic purposes, particularly when a person cannot urinate normally. The document discusses various types of catheters, complications, contraindications, and step-by-step procedures for catheterization in both males and females, highlighting the importance of maintaining sterile techniques to prevent infections. It also outlines the necessary equipment and common errors to avoid during the procedure.