Induction is like when you are building a tower out of blocks. You start with one block and then add another block on top of it. Then you can add another block on top of that one, and keep adding blocks until you have a really tall tower. Induction is a way of proving things that works like building a tower. You start with something that you know is true, and then you show how you can build on top of it to prove that other things are true too.
Bounding is when you put a fence or a barrier around something to keep it from going too far or getting too big. Bounding is a way of controlling things and making sure that they stay within certain limits. For example, if you have a ball that bounces, you might put a fence around it so that it doesn't bounce too high or too far away.
The least number principle is like trying to find the smallest number that works for something. Imagine that you have a bunch of boxes and you want to pack them into a truck. You want to use as few trucks as possible, so you try to find the smallest truck that can hold all the boxes. The least number principle is a way of finding the smallest amount of something that you need to make something work.
All three of these things can be used together to solve problems and prove things. For example, you might use induction to prove that a certain pattern works for all numbers. Then you might use bounding to show that each number in the pattern is not too big. Finally, you might use the least number principle to find the smallest number that the pattern works for. Together, these three things can help you solve tricky math problems and figure out how things work.