Auto-Lock cells after entry

Try this

Private Sub Worksheet_Change(ByVal Target As Range)
    Dim res As Integer
    Const sPW As String = "secret"
    With Target
        ''/// do not run if selection more than one cell
        If .CountLarge > 1 Then Exit Sub
        Me.Unprotect sPW
        res = MsgBox("Are you satisfied with the entry?", vbQuestion + vbYesNo + vbDefaultButton2, "Save entry")
        
        If res = vbYes Then
            .Locked = True
        Else
            Application.EnableEvents = False
            .ClearContents
            Application.EnableEvents = True
        End If
        Me.Protect sPW
    End With
End Sub

Before setting up the code you need to prepare the sheet. All cells must be unlocked and a password applied to the sheet to make the locking of the cells effective. If you aren't sure then read this.

The code is worksheet event code so read this to understand how to enter it.

Where to put the code

Did you unlock all the cells before starting as I suggested?

Select all the cells by clicking on the triangle in the top left corner(between A & !. This will select all cells. Right click on any cell and choose Format Cells-> Protection and uncheck Locked.

All the cells will now be unlocked. Lock any cells that you want to protect then apply the password.

The code will not lock cells if you choose No.