LEFT SIDE
The dimension on the left is the overall width including the gutter.
The small dimensions in grey are the purlin spacings.
RIGHT SIDE
The dimension on the right is the frame width.
To change the width or length, you can choose the Shapes/Dimensions tab and alter them here.
Or you can select the dimension on the workspace and change it there.
BOTTOM
The dimension along the bottom is the frame length.
The grey dimensions above the frame length are the rafter spacings.
The grey dimensions above this are the distances between the posts.