Using the Import Wizard - Screen 1 - Define Fixed File Field Layout

If the Source Type is fixed-file, then a Define Field Layout screen appears to set the column positions and field lengths.

Below the print screen is an explanation:

Column Position: This is the first position of the column.

Field Length: This is the length of the column (field).

Click Add new row and enter the first column position and field length.
Press Tab or Enter to activate the Delete Selected rows and Add new row, then click Add new row to continue.
Continue adding new rows and values until all fields are mapped.
Click Save to save the file layout and click Next.