Hi there i recently discovers your wonderful app and start using it. but I have a some questions about the study process:
Welcome to Skritter! 
In a nutshell, when you grade an item as correct and it’s 100% due, it will be scheduled roughly twice as far away as the last time you had reviewed the item, and marking something as wrong resets the scheduling so you can start reviewing it more and remember it again. If you’re noticing items cycling too quickly in the beginning, I recommend marking them with “too easy” (4), which pushes the next review much farther away than the standard (3) grade button. Here’s a link to some more information on the scheduling system: http://docs.skritter.com/article/51-spaced-repetition
On the legacy website (https://legacy.skritter.com), you can go inside of a list and then section, which shows a green circle next to each word that has been added, even if they were added from other lists, while words that haven’t been added won’t show the green indicator. This is still in the works for the beta site / app, however in the meantime, you can view a list of all your words on the 2.0 site, at: https://skritter.com/words
A study session is typically over when you reach zero (on the items due counter). In the beginning of course, you’ll want to add as many new items as you’ll typically want to review in one day. The idea is to Skritter consistently so the review queue is predictable and steady. Ideally, you want to review items when they are 100% due, and not overdue or underdue.
If you have any more questions be sure to let us know!