In modern view, click on the gear in the Reports widget, select 6 months or last year, then when you move your mouse over the bar graph it will give you your miles for the month. If you have multiple activity types you will have to deselect them to get running only. If you select the calendar, you can see activity count, miles, time, and calories at the bottom.
You can also go to classic view and filter your activities by any type and any date, get a list, and even export to a spreadsheet if you like.
You can click the three horizontal bar icon on the left edge of the screen near the top. Then click the word Reports in the slide-out menu. Sometimes this page won't load the first time. You may have to click the refresh button (or press F5) to get the page to load properly. Once the reports page loads, scroll to the bottom and click the Progress Reports link. Configure the report to your liking (probably Group by Month, This Year, and Running).
Travis