In later versions of the beta, and in the final release, you'll be able to add your own sentences, and we're creating a web app to allow you to do that and record those sentences easily with the help of a tutor or language exchange partner.*
Although the app will not support adding vocabulary as in single words separate from the sentences, theoretically you can add a "one-word-sentence" if you would wish to add a single word to your cards for review. But we would recommend that you switch to full sentences after learning the 625 stand alone words that we have put in the app.
* Note that you'd find those native speakers on another website; we're not supplying them as of yet.