Get Monthly and weekly Report Details in SQL Server

hi friends

i have table and one of my columns is "date_save".

in this field i have date and time as below :

2018-02-25 19:38:42.497

i get this by GETDATE() in sql.

my table is as below :

CREATE TABLE [dbo].[Customers](
	[id] [int] IDENTITY(1,1) NOT NULL,
	[countt] [int] NULL,
	[flbuyer] [nvarchar](50) NULL,
	[date_save] [datetime] NULL
)

Now I want to get the table output based on "sum(countt)" last month and last month (From today to the last week and from today to the last month)

my language is VB.Net

thanks