The motto "Evolution is a fact" requires a detailed explanation. Otherwise, it can be taken different ways by advocates of different points of view, leading to confusion; see Define your terms.
Changes in populations of species
Sometimes, "Evolution is a fact" refers to the common observation that the number of individuals of a certain species varies with time in a certain range. For example, the wolf or rat population tends to increase whenever and wherever human beings establish ranches or cities. More sheep, more prey for the wolves. More garbage, more food for the rats.
Natural changes, such as desertification generally reduce populations. In general, ecology studies how animals and plants increase or decrease their prevalence in the various regions on earth and underwater.
So, the observation that the size and extent of a population can change over time, varying with climate and other conditions, is rather straightforward and uncontroversial. People who hate wolves and rats know that if they don't feed them, they'll go away. But if they leave sheep unattended in unfenced pastures, wolves will come. Populations of species of animals grow and shrink in response to the environment, as do trees and other plants.
Changes in body plan
At other times, "Evolution is a fact" refers to the less frequent observation that a population has changed in visible ways. For example, there may be more spotted or black sheep in a herd. Jacob noticed this, when he was working for his uncle Laban. Religious scholars generally see this change as a response to Laban's attempts to cheat Jacob.