When we talk about the word penetrate, think of a key that fits into a lock. The key goes inside the lock to open a door. Just like that, penetrate means going inside or through something.
Imagine a straw in a juice box. The straw goes through the top of the box so you can drink the juice. The straw is penetrating the box.
Think about a plant growing in the ground. Its roots go deep into the soil to find water and nutrients. The roots are penetrating the soil to help the plant grow.
Consider the way a needle goes through fabric when sewing. It moves in and out to keep pieces of fabric together. The needle is penetrating the fabric.
Finally, picture a sunbeam shining through your window. The light goes through the glass and fills the room with warmth. The sunbeam is penetrating the window.
So, whenever you hear penetrate, remember it means something going inside or through another thing, like keys, straws, roots, needles, or sunbeams.