Microscopy
Microscopy is using a tool with lenses to see things too small for your eyes alone.
Think of it this way
A glass jar of water with tiny dots of food dye looks plain from across the room. Hold a round magnifying glass close to the jar and those dots appear as large, clear circles. A microscope does the same thing with a stack of lenses that bend light. The tiny object does not change; only what your eye sees does.
Explaining microscopy by grade level
Your eyes cannot see the tiny parts that make up a leaf or your skin. A tool with a glass lens makes those parts look big. When you look through it, you can see small round shapes called cells. Every living thing is made of these shapes.