This is a representation of how the instance list will appear when the business object executes. You can use it to change the order the columns appear in, and their width.But remember that these are only the initial values. The user will be able to rearrange and resize the columns, and those values will be remembered for that user.
You can change other properties of the columns by clicking on the column and editing values in the prompter:
You can also delete a column in the prompter.
This is an option on the Instance List Column Maintenance Panel.