Every day, week, section, and memory verse page has a Mark Complete button. Click it once you have actually done the reading, not before. The button remembers the date, and nothing about it disappears if you leave the page.
Come back to the home page and you will see it again, without having to look for it. Once you have completed even one step, the study card for that study grows a small progress bar: how many steps you have finished out of the whole study, and where you left off.
That last part matters more than the percentage. You do not have to remember where you stopped. Open the site, click your study’s card, and it takes you to the next thing, not the beginning.