The foundation is the lowest part of a building, often below ground level. It is usually the first part to be built and the most important because it holds up the rest. We can also use foundation figuratively to describe the fundamental basis or belief of something. For example, the teachings of Jesus are the foundation of Christianity. In both cases we talk about starting the process of constructing a building or explaining a new idea by laying the foundation(s).
Our house is still being built. It's going to take a long time, because they have only begun to lay the foundations. They dug a hole last week and have built a basic structure there now.
Darwin's theory of natural selection is the foundation of modern biology. Biologists today begin with evolution and natural selection to imagine and describe how living things develop and change.
An organization that is created to do charity work or improve society is often called a Foundation. Foundation comes from the verb to found, which means to start something. We usually found cities, businesses, schools, and institutions and talk about it in the passive voice. For example, Michigan State University was founded in 1855.
The Guinness brewery was founded in 1759, when Arthur Guinness began brewing beer there. So the company has been brewing for more than 255 years.