
You can get
“The beginning and end of this month”!

Use the following function:
Date function
Month function
Year function
DateSerial function
VBA Code
As an example, get The beginning and end of this month.
Option Explicit
Sub sampleProc()
'Get "beginning of this month"
MsgBox (DateSerial(Year(Date), Month(Date), 1))
'Get "end of this month"
MsgBox (DateSerial(Year(Date), Month(Date) + 1, 0))
End Sub
Result
You got “The beginning and end of this month”!
※Due to the Excel settings, the result is in Japanese notation.


FYI
For more information about following, see the following official online manual:
●Date function
●Month function
●Year function
●DateSerial function