What is the meaning of the idiom "To make a mountain of a molehill"?

The idiom "to make a mountain out of a molehill" means to give great importance to little things. It is often used to describe someone who is overreacting to a situation or who is making a big deal out of something that is not really a big deal. The idiom comes from the idea of someone who is making a small pile of dirt (a molehill) seem like a large mountain.

The other options are incorrect. "To get into trouble" does not mean to give great importance to little things. "To see a thing with prejudiced mind" means to see something with a preconceived opinion, which is not the same as giving great importance to little things. "To grow bigger step by step" means to increase in size gradually, which is not the same as giving great importance to little things.