Stacynak, I know, it can be confusing. If you have a MB, then you picked your three FP+ selections beforehand. After you've used them, you're eligible for another that must be selected at a FP+ kiosk in the park (and that doesn't have to be the same park your others were in). But you do have to stand in line. The additional ones aren't available via the MDE app. Keep in mind that to get an additional FP+ at a different park, you have to hop to that park first and make your selection from a kiosk there.
People who buy single-day tickets ONLY have the kiosks to make their selections from what's left in the pool after the MB resort people made their advance selections. Hence the lines in the front part of the parks. I've heard that lines are shorter at kiosks further in though.
I hope this helps...