Are you looking to get the first line directly from the TextBox or from the database? If it's the former, the Lines property of the TextBox returns the lines of text as a String array, so you can simply get the first element. If it's the latter then you can use String.Split to split the text on line breaks to get a String array.
Note that, in a TextBox, line breaks consist of a carriage return and a line feed. Use Environment.NewLine to represent the line break when calling String.Split, which means that you MUST use an overload that supports Strings rather than Chars to split on.