Pretty easy once you get the hang of it, The incubation period for chicken eggs is usually 21 days. The most reliable way to incubate your fertilised eggs and maximise the chance that they will hatch into healthy chicks is to use an artificial incubator.
Also this link may help https://www.durhamhens.co.uk/hatching-guide
Also this link may help https://www.durhamhens.co.uk/hatching-guide