Simple columnar epithelium is a single layer of tall, column-shaped cells whose main jobs are absorbing and secreting substances. OpenStax Anatomy and Physiology notes that it lines parts of the digestive system, such as the stomach and intestines, where it takes up nutrients and releases secretions, and parts of the female reproductive tract.
Some of these layers include mucus-producing goblet cells, and a ciliated form found in the fallopian tubes and parts of the respiratory system uses beating cilia to move material along and clear away particles.
Source: OpenStax Anatomy and Physiology 2e: 4.2 Epithelial Tissue
Image: simple columnar epithelium with a goblet cell, Berkshire Community College Bioscience Image Library, CC0, via Wikimedia Commons.