Okay kiddo, so you know how Scotland is a country, right? Well, Scottish devolution is when the Scottish people got more power to make their own decisions about things that affect their country.
Before devolution, decisions about Scotland were mostly made by the UK government, which is the government for the whole United Kingdom (which includes Scotland, England, Wales and Northern Ireland). But Scottish devolution means that now Scotland has its own government, called the Scottish Parliament, that can make some decisions for itself.
The Scottish Parliament gets to decide things like education, health, and transportation in Scotland. This means that they can make rules and laws that are specifically for Scotland and that fit the needs and wants of the Scottish people better.
However, there are still some things that the UK government has control over, like defense and foreign affairs.
Overall, Scottish devolution means that Scotland has more control over its own affairs and can make decisions that are best for its people, while still being a part of the UK.