That's a great question! A hypothesis is an educated guess about what you think will happen in an experiment.
For example: Let's say you are performing an experiment on pea plants, and you have some plants that will get fertilizer and others that will not get any fertilizer, and you want to see which plants will grow taller. You believe that the plants that get fertilizer will grow taller than the ones that get no fertilizer, so your hypothesis is: Pea plants which get fertilizer will grow taller than pea plants that get no fertilizer.
It's OK if your hypothesis is wrong, too. You are just guessing about what you think will happen.
For example: Let's say you are performing an experiment on pea plants, and you have some plants that will get fertilizer and others that will not get any fertilizer, and you want to see which plants will grow taller. You believe that the plants that get fertilizer will grow taller than the ones that get no fertilizer, so your hypothesis is: Pea plants which get fertilizer will grow taller than pea plants that get no fertilizer.
It's OK if your hypothesis is wrong, too. You are just guessing about what you think will happen.