Watch the Week 1: Intro to Master Structure I online guitar lesson by Les Wise from Fretboard Freedom Fighter
A "master structure" is much more than an arpeggio. It is a system for playing the arpeggio types from every finger and string. It is very important to really master this first one. Everything else in the course is based off this structure. Get this right, and everything else will be much easier.
Remember: Our goal for the course is just one thing, master the 3 structures!