How to construct a hypothesis?

Well, you have to have know theories that you know. An hypothesis is what arises when you put all what you know to predict something.

Like... you know that like poles in a magnet repel. So, you think about magnets and ask for example this question. "What if I put the like poles of two magnets, one being on the floor and the other one right above it?"

Well, looking back at your theory, they should repel. So, you think that the one above the former magnet should float. So this is a hypothesis.

Then you carry out experiments to verify if your hypothesis is true. If not, then you try to see where you went wrong, or where there needs to be other factors to be considered.

I hope it helped! :)