First you need to import the library which is required to handle Excel files. Doing so will allow you not only to import Excel files, but to edit and save (create) them.
Use:
Imports Excel = Microsoft.Office.Interop.Excel
at the beginning of your program.
There are 3 elements you need to set to something, in order to access the Excel file:
Excel.Application - for the entire Excel interfacing
Excel.Workbook - should point to the actual Excel file (.xls or .xlsx)
Excel.Worksheet - should point to the worksheet you with to import from.