Welcome to the Forum!
The GB App Graph Information is:
Red Line - Highest Reading - Of the Day
Purple Line - Calculated Average - Of all data input during the Day
Blue Line - Lowest Reading - Of the Day
Read through the first three threads in the Type 2 Section, when you get a chance, if you have not already done so. These threads will most-likely help you a lot. Self education is one of the keys to successful management of your diabetes, along with a healthy / sensible diet and exercise. Basically, diabetes requires a life-style change for the better. Good luck with your control and management.