On the dashboard (main page) under Mastery Schedules, you'll see "manage your schedules" at the bottom. Tap there, then on "all schedules" then on "beginner". Tap on the plus sign next to "beginner Japanese / N5" to add it to your schedules. The grammar is linked with the vocabulary so you will see both added. Otherwise, you can search for N5 vocabulary in the community lists and add one from there.