Just like this:

I assume from the UI: the upper input field is the name of the things i create. And with the button next to it i confirm the action. The create thing then lands in box below.

Okay i know the first is the password, the button is password generation and the last is the secret text input field, or what ever we want to call it.
Suggestion:
- Add password
- Gen. – short for generate –, Generate or dice icon
- Write your secrets here, Fill me with secrets, etc.
PS: Owncloud does not use a checkbox, but:
