copy the first or target cell and paste it onto the next cell(s) below

Not much to go on but assuming you target cell is in "A1" and that you want to loop down or by rows, add the following code to the Worksheet module...

Option Explicit 'keeps you from making simple mistakes
Private Sub Worksheet_Change(ByVal Target As Range)
Dim i As Integer
If Target.Address = "A1" Then 'replace "A1" with you target cell
    For i = 1 To 100 'begin loop from Start row to end row number
        If ActiveSheet.Cells(i, 1) = "" Then     'If the next cell is blank then...(.Cells(row,column)...1 is column A and B=2, and C=3 etc...replace with whatever column works for your application
            ActiveSheet.Cells(i, 1) = Target.Value
        Else ' if the next cell does contain a value
            Exit For 'exit the loop
        End If
    Next i
    
End Sub

Hi! I don't know why but I can't upload the file so please bear with me. thank you again! so basically, I want to copy the year
2017 and paste it onto the next cell below it until it reaches the year 2018.sample.PNG

Welcome to the forum
Can you upload sample workbook to find solutions quickly?