Observation use your senses that you are observing plants in your garden.
problem then a question may came up into your mind why is this plant dying?
hypothesis you could answer that the plant is dying because there is too much sunlight.
test you will setup a plant where there is too much sunlight this is the experimental setup and the one with just enough sunlight will be the control setup.
theory the plant which you placed with too much sunlight died and the one under little sunlight survived, then your hypothesis is right and you have now the theory.