The app doesn't have any concept of "show you X new cards each day".
The "max new cards" is the number of cards in your "new card" group.
Say you have 100 flashcards. The all start in a "pending" state. By default, max new cards is 10, so I'll assume this. 10 cards (the first 10 by default) are chosen as "new cards". You enter the deck and choose to study "new cards" and these 10 cards are shown to you. These 10 cards will be repeated continuously until you either answer a certain card correct 3 times in a row, or swipe up once. (If you swipe up, a "new" card will immediately become "active" and will be tested again in 3 days, vs the normal 1 day.) After the card moves to "active" status, the next "pending" card becomes "new" so that you again have 10 new cards.
The max new cards defines how many cards you are practicing at once in new-card mode. More cards means potentially harder to remember a card the next time it shows because it shows up less quickly.
As you study new cards, a summary screen should tell you how many new cards you've moved from new to active status. So you can use this information to determine when to stop for the day (e.g. you've moved 30 cards from new to active). Keep in mind that you'll be studying more than 30 cards each day in this case.
If you want to limit yourself to seeing exactly 30 cards, you can go to Deck Options > Cards to Study > Card Range and limit your range to the first 30 cards, and increase by 30 each day, but I don't think it's that great of a solution because as you get to the last few cards, you'll be repeating them very quickly. The purpose of my "new card" mode is to make sure you can remember them after say 5 minutes (x 3) so that when they are shown after 1 day (first scheduled repeat once they become active), you have a chance at answering.
Studying "due" cards is a different mode, so backup to main deck screen, re-enter deck, and you'll have the option to study due cards. When no more due cards, go back to learning new cards.
http://orangeorapple.com/Flashcards/AboutSR.aspx