Yes, everyone can contribute to science in their own small way. The best way to contribute to the science and enhance our knowledge is by carrying out research in our scientific discipline of interest. There are several areas of science (including physics, chemistry, biology, astronomy, zoology, botany, environmental science, etc.) and you can contribute to any. One does not have to have a doctorate or masters degree to contribute. For example, if you calculate the amount of organic waste that is being generated in your kitchen daily and try to compost it and calculate the quantity of compost that can be sustainably generated every week or so, you have done your part. Now we know how much compost we can generate weekly (or monthly) from a home (in rural/urban area, etc.). You can share your results online and you have contributed to the knowledge of community, and that's what science is. Another project could be the savings in carbon dioxide emissions by change of habits (say, less drive, more walk; changing to higher efficiency appliances; use of organic food; less packaging, etc.) and accompanying cost (or savings) estimate for your home. Small projects add up and enhance our knowledge and that way we all can contribute to science.
Hope this helps.
Many large scientific projects rely on 'citizen science'. This is a term that refers to someone who is a non-specialist in science that collects data and submits it to a database, usually through the internet or an app. An example would be the website ebird.org where anyone can submit information about bird sightings. Scientists have access to this information and can use it to understand things like population numbers, or migration routes. Some more citizen science based projects are Project Feederwatch, The Great Sunflower Project and Monarch Watch.
Yes! Everyone who sincerely tries can have an impact on science. Science is a broad field of study encompassing many different aspects such as biology, chemistry and physics. The least one can do for science is research. Research can be performed in a myriad of ways. It can be as simple as recording the eating habits of animals or performing more complex psychological analyses of patients. If you do research and submit it onto the Internet or somewhere accessible, you are helping to build and further the community of science. Even if your contribution seems small, everyone starts from somewhere and every little bit helps.