Filter SQL query using parameters

It depends on how you are setting those values. I use queries as a scalar value for this. So I might have a query that simply evaluates to = #date(2021,3,1), then I have a simple query like this:

let
    Source = Sql.Databases("localhost"),
    ContosoDW = Source{[Name="ContosoDW"]}[Data],
    DaxBook_Sales = ContosoDW{[Schema="DaxBook",Item="Sales"]}[Data],
    #"Filtered Rows" = Table.SelectRows(DaxBook_Sales, each ([Order Date] >= varStartDate))
in
    #"Filtered Rows"

Power Query will then fold that and send this SQL statement to the server for processing:

select [_].[OnlineSalesKey],
    [_].[StoreKey],
    [_].[ProductKey],
    [_].[PromotionKey],
    [_].[CurrencyKey],
    [_].[CustomerKey],
    [_].[OrderDateKey],
    [_].[DueDateKey],
    [_].[DeliveryDateKey],
    [_].[Order Date],
    [_].[Due Date],
    [_].[Delivery Date],
    [_].[Order Number],
    [_].[Order Line Number],
    [_].[Quantity],
    [_].[Unit Price],
    [_].[Unit Discount],
    [_].[Unit Cost],
    [_].[Net Price]
from [DaxBook].[Sales] as [_]
where [_].[Order Date] >= convert(datetime2, '2021-03-01 00:00:00')

varStartDate (you can call it whatever you want) can be hard coded, dynamic based on today's date - =DateTime.Date(DateTime.LocalNow()), or any other date logic. It can also be based on values in another query, so 

= List.Min(
    List.Buffer(SomeQuery[Order Date])
   )

Would return the earliest date from the order date field of SomeQuery. You could further manipulate that with Date.StartOfYear, etc.