Science is a big umbrella term that encompasses all sorts of disciplines that are concerned with our world and the living and non living matter that populates it.
I would say that the 10 main sub branches of science would be:
- Astronomy: studies the Universe, its compositions and movements in terms of planets, stars, galaxies and so on.
- Biology: it is the study of life concerned not only with humans but also with plants, animals and other living forms on the planet.
- Botany: studies that cover plants and their lives
- Chemistry: studies the matter at a more microscopic level because it looks at its particles and how they act, exist and combine together.
- Ecology: studies the relationship that living organisms have with each other and their environment.
- Geology: studies the planet Earth and how it is composed and structured
- Meteorology: studies the atmosphere in order to predict weather changes and forecasts.
- Oceanography: studies water's movements, currents, waves and tides as well as composition and its life.
- Physics: it basically studies how the universe work by exploring the laws and rules of the matter, its motion, energy but also space and time.
- Zoology: studies that cover animals and their lives
However, these can also be divided in other sub-branches accordingly to their areas of interest. The majority of them are also linked with each other (think about physics and chemistry with biology, or oceanography for example).
Plus other sub-branches of science could be studies that are not purely scientific but deal with human life and behaviour. If you think about communication sciences, social sciences, forensic sciences, psychology and so on.
Similarly, medicine, agriculture and computer science might be added to that list because the principles of those main sub-branches are applied to them. As you can see the term is pretty wide and includes all sorts of different aspects of life and the world in general.
Alternatively you could also look at this similar question and the answers that were given.