How do I import notes from Plaintext files?

Open the Notesnook app (web or desktop)
Go to Settings > Import & export > Notesnook Importer and select "Text".
Drop your .txt files, or click anywhere inside the box to browse and select your .txt files. You can also provide a .zip file containing all your .txt files. Then click "Start importing".
Once the importing completes you should see all your notes in Notesnook. If you face any issues during importing, feel free to report them on GitHub.

Importing notes — every app and file format Notesnook can import
Import from Evernote — moving notes out of Evernote
Import from Google Keep — moving notes out of Google Keep
Import from Joplin — moving notes out of Joplin
Backup and restore — protecting your notes once they're in
How is my data encrypted? — what happens to your notes after the import