The knowledge, methods, and everything else regarding the understanding of the Cosmos. This includes essentially structures based on logic (and Mathematics, in general) that must match what is observed in the Cosmos. See The Scientific Method-Richard Feynman, and Philosophy of science
"Science is the attempt to set in order the facts of experience." ~ Buckminster Fuller
Map of science. Science ontology
Lay the concrete foundation for the rest of the sciences, by looking at fundamental structures and ideas. From the more theoretical to the more applied:
Philosophy of science -> Mathematics -> Theoretical computer science -> Mathematical methods and Scientific computing
Portal:Contents/Mathematics and logic
Natural science is often defined as the part of science studying natural phenomena (that is, those not cause by Humans). These are in some sense, the foundational sciences, as everything (including Humanity) is ultimately part of Nature (the Physical world).
Roughly, we can categorize the natural sciences, in order of the complexity of the studied systems, forming a sort of hierarchy, or emergent new phenomena:
Physics -> Chemistry -> Biology -> Cognitive science
Portal:Contents/Natural and physical sciences
Systems sciences studies very complex natural phenomena, as well as human phenomena (which are of course, a result of natural phenomena, but often of the highest complexity we know). It is the application and integration of the more reductionist ideas of the foundational sciences to larger systems.
Systems Sciences are the highest level of complexity, looking at parts of the Cosmos made of many parts interacting in complex ways.
Some of the most important ones are Social sciences, which look at societies (large collections of complex agents).
Portal:Contents/Society and social sciences
The distinctions above are fuzzy, and a bit ambiguous. This is partially because of the History of science being very complex, and with conflicting ideas of how science should be organized.
However, as can be seen from above, my preferred way of organizing it is an approximate hierarchy of complexity: from simple (reductionist) laws to complex systems.
Wikipedia:Portal/Directory/Science and mathematics
Thaumaturgy in the Age of Science by Prof. V. Balakrishnan
Free MIT books: https://archive.org/details/mitlibraries
Crowdfunded science: https://experiment.com/
"How to science": videos in channel: https://www.youtube.com/user/Taylorns34
Check if there are papers refuting or contradicting a given one: https://scite.ai/