You’ll move onto each level after you’ve filled the bar under each kanji. Then, on the next level, you’ll fill in the bars for the kanji for that particular level. I.E. On level 1. You’ll fill the bars under each kanji and then level up (after passing the required amount). Then you’ll see new kanji in level 2. And you’ll do the same process. Hopefully this is clear?
After you’ve gone through the official Wanikani FAQs. Check out this guide: My Journey of 368 days (+ The Ultimate Guide for WK 
)