Looping

[montecarlo2012]

Hi, everyone, merry Christmas and thanks all you for your time and teaching I got from you.
I am practicing a little bit about loops, so trying to sum rows by rows I got this

Sub addrows()
Dim x As Long 'ROWS
Dim y As Long  'COLUMNS
 For x = 1 To Cells(Rows.Count, "A").End(xlUp).Row
 For y = 1 To 3
 
 Cells(x, "H").Value = Cells(x, "H").Value + Cells(x, y).Value
 Next
 Next
 
End Sub

what about if I want to sum column by column like for example

1	4	7
2	5	8
3	6	9
6	15	24

and what about if I want to sum a column two number each time I go down, example

	1
	2		3
	3		6
	4		10
	5		15

I want to understand how to loop operations . thanks.