These are the part of ancient living organisms which are preserved or traces in rocks.
Use of study of fossils:
The study of fossils broadly called paleontology helps in understanding important phenomenons like how life originated on Earth, changes in climate, lifestyle and culture, etc.
Apart from this paleontology helps in studying the evolution of various species which forms a good base of research to understand life and living forms.
Understanding age-old techniques, traditions, and civilization may help in composing better solutions in the future, and thus the study of fossils helps in getting a futuristic outlook.