how to create new folder

Directly creating folders within the app is not currently supported.

To add a new folder, login to your web mail and create the imap folder or label. The new folder will then be available within Thunderbird for Android after refreshing it's folder list.

To refresh the apps folder list.

1. Open the side bar with your account folders displayed (Inbox etc).
2. Tap manage folders (bottom of list).
3. Tap the three dot menu > refresh folder list.

The community have been voting on Mozilla connect for the feature to create imap folders within the app. You can show support by up-voting the idea below.

https://connect.mozilla.org/t5/ideas/add-the-ability-to-create-imap-folders/idi-p/72777