Spirals are curved lines that grow bigger and bigger from the center.
I don't know how to relate your question specifically to arts and crafts without further information.
A spiral galaxy is a "spiral" without a physical bar structure. Whereas a barred spiral galaxy has an obvious central bar. See related pictorial for a better idea.
Galaxies are the shape that they are because of the way the gas and dust that made them were moving. When relatively stationary gas and dust begin to coalesce, the result is irregular or globular....