By going to the "New Release" page you can select titles that will show up in your "Pull List".

You can review your titles by the publish date.  When you purchase the comic book or change your mind, deselect the check box and tap save - you will be prompted to add the issues to your collection or delete.  Keep in mind there are 3 required fields: Publisher, Title and Issue Number.  Some items in the New Release list may not have an issue number.  If you try to add an item with out an issue number you will be notified and given options to cancel the removal.