When cell changes, execute code

Hi,
Pretty much when cell J26 changes (it is linked to another cell), I want it to execute [Sub MRP_trickledown].
I did some searching but wasn't completely sure on how to use this

Private Sub Worksheet_Change(ByVal Target As Range)

If Not Intersect(Target, Range("J26")) Is Nothing Then
 
[copy/pasted sub MRP_trickledown] 
    
    
End If

Also, does it matter where I put the private sub?