Decks are created from a single modal, reachable from two places in the app. This article covers the fields in that modal and what happens once you save.
Opening the modal
The most direct way is from the 
Decks tab: tap the plus button in the top-right corner.
You can also create a deck from inside the deck selector on the 
Translator screen. Tap the deck name in the header to open the selector, then choose the option to create a new deck. See Choosing a deck for how the selector itself works.
Both paths open the same "Create new deck" form.
Fields
Deck Name
Required. This is the only field you must fill in to save.
Deck names must be unique within your account. Two decks can't share the same name.
Description
Optional. A free-text note about what the deck is for. Nothing in the app depends on this field; it's for your own reference.
Review Mode
Review Mode controls the direction cards are shown in during study: which side is the front, which is the back, and whether that follows your native or target language rather than however you typed the card. Four modes are available, shown as a grid: Normal, Reversed, Native on front, and Native on back. Normal is selected by default.
Normal is free. The other three modes require flangu Pro; tapping one without Pro opens an upgrade prompt instead of selecting it.
Warning
Review Mode can only be set here, at creation. It cannot be changed afterward. What each mode actually does is covered in Deck settings.
Settings
Three more settings sit below Review Mode, each shown as a row with its current value and a "Default" badge when left unchanged:
| Setting | Default | What you do here |
|---|---|---|
| Retention | 90% | Tap the row to open a picker and choose a target retention percentage. |
| Max new cards/day | 20 | Tap the row and enter a number from 0 to 9999. |
| Max reviews/day | 200 | Tap the row and enter a number from 0 to 9999. |
What these settings actually change about your studying is covered in Deck settings. You don't need to touch any of them to create a deck; the defaults are used if you leave them alone.
Saving
Tap the confirm button in the header to save. The button stays disabled until you've entered a name.
A "Deck created successfully" confirmation appears, and the modal closes. What happens next depends on where you opened it from:
- From the Decks tab, you stay on the tab. The new deck appears in your deck list right away.
- From the Translator's deck selector, you're returned to the Translator screen with the new deck already set as your active deck, ready to add cards to.
Either way, the deck starts empty. Cards are added to it separately, as described in Creating a flashcard.