Circular From

This is original circular form. 
From Jiang Rong Qiao (also anglicized as Chiang Jung Ch'iao)
He was the first of the Bagua masters to create one main form from all the shorter forms and drills.

So this is now our mother form in Bagua, and should be learnt first.
Where to start:

Bagua Complete Basics Series is the place to start here 
Then go onto the "Advanced Bagua Circular" series.
Along with this you will find MTG 316, 455, 38 and 39 very insightful. 
Then the rest of the "Essentials" Series and "To the Max" will give you different ideas looking at the form and seeing Erle move is something special as well.