When looking at your data, you have several ways to quickly pick a time range.
Pre-defined: the date range is selected for you, you just have to click on a pre-defined filter. For example, last month, or yesterday.
Relative: choose the number of days you would like to go back on the days. For example, last 180 days.
Date Range: select the time range that you want.
You can use this filter to choose how you want to aggregate the data.
For example, if you select a 3 weeks time range and choose a month aggregation. This will sum up the data of the last 3 weeks.