。
The leaves were whirling around in the garden.
Literal
Tree-[possessive-の]-leaves [subject-が] garden [at-で] whirl-whirl was-dancing.
くるくる is a mimetic for light, repeated circular motion — spinning, twirling, rolling. Here it modifies 舞う ('to dance, to flutter'), a poetic verb used for anything light and airborne moving with grace. Pairing a mimetic with a descriptive verb is the standard way Japanese captures visual texture.