The physical distinctions are definitely the biggest difference. I assume you’re referring to the gray squirrel and the eastern chipmunk. Gray squirrels are much larger, gray with white undersides, and long bushy tails. Chipmunks, meanwhile, are small enough to fit in the palm of your hand and are a glossy golden-brown with conspicuous stripes running down their backs.
The other big distinction between them is their living habits. While gray squirrels are heavily adapted for arboreal lifestyles, chipmunks will dig elaborate burrows in the ground, sometimes with multiple entryways and escapes. Chipmunks are also capable of climbing trees, but they prefer to stay on the ground, while squirrels come down to forage but nest in, sleep in, and flee to the trees.