1. Tap the "Manage your schedules" link on the dashboard (below your current schedules)
2. Create a new schedule, name it whatever you'd like.
3. After making it, it'll say "hey, there are no materials for this schedule", and you'll be able to add materials
4. The Adjust materials page looks very similar to "Learn > Lesson Center" - you can search for lessons here and add them to your schedule.
To get to the JLPT stuff, just tap the "made by renshuu" link below the search bar, or you could enter "JLPT N3" and you should see the materials pop up.