Jeffrey,
What you are needing is not specific to the report designer and rather part of the SQL so it is not shown in the videos. What you need to use is the SQL function Current_Date which you enter in rather than a specific date as it will read the date from the system.
As you also mentioned wanting a date range, this can be achieved by first specifying the operator Between and then the following value (assumption is that you want the past week):
Current_Date - Interval '7' Day, Current_Date
You can vary the above as necessary as long as you keep with the format
Start Date, End Date