Microsurgery is when doctors use special tools to work on very tiny parts of the body, like blood vessels or nerves. Imagine you have a toy car with very small parts that need to be fixed. Instead of using your hands, you need to use tiny tools like tweezers or a magnifying glass to make sure you don't break anything.
Now imagine a doctor needs to fix a tiny blood vessel in your finger. They would use a microscope to make the blood vessel look bigger. Then they would use tiny tools, like a needle and thread but much smaller, to sew up the vessel. It's like doing surgery under a super zoom lens, so the doctor can see everything clearly.
Microsurgery is used for a lot of things, like repairing nerves after an injury or even reattaching a finger if it has been cut off. It is a very delicate and precise kind of surgery and requires a lot of skill and training.