This is a pretty basic and self explanatory error. If you are copying and pasting code without attempting to understand what it does you are doing yourself a disservice. A simple google search and you would have more than likely resolved this error on your own which would have also helped you learn how important figuring things out on your own is.
Given I don't know anything about your project nor did you provide much of a code snippet I can only assume you are using a data grid view.
If you reference this link
DataGridView.DataSource Property (System.Windows.Forms)[
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There is a code snippet that shows you how to declare a data grid view which is what the error you are running into.