The Reading Log allows you to track WHEN you read a comic alongside your ratings and reviews. To add an entry:
From any comic, click the menu (three-dots icon) to open the My Details modal. Here, select the Reading tab and then enter in the date you read this comic. When the date is selected, click Add next to it. Follow that by hitting Save and Close. You're all set.
From the mobile app, this can be done from any comic's menu. Simply select Log Last Date Read and pick your date.