Working On File Opened With GetOpenFile (VBA)

the small code i'm writing just needs to do the following:

1. open an .xslx file selected by the user
2. copy 2 worksheets from that file to the current one
3. close the selected file without saving it.

This is my code:

VB:
Sub GetData()
MsgBox ("Please select a file"), vbOKOnly
Master = Application.GetOpenFilename(FileFilter:="Excel Files (*.xlsx), *.xlsx", Title:="Please select a file")

[Code]....

Opening the file works, but the last 3 lines don't because i don't understand how to declare "Master": however i dim it (workbook, object, variant...) i get an error on the GetOpenFilename line. If i don't declare it, i get an error while trying to copy the worksheets.