Input: yellow pulley of D1 diameter.
Output: pink pulley of D2 diameter. D1 = 2*D2
So the output speed is twice the input speed.
The input and output shafts are perpendicular to each other.
The orange idler pulleys guide the black round belt between the input and output pulleys and prevent the belt from leaving the pulleys.
Move the blue pulley bracket up to tension the belt. Use the green bolt to clamp the bracket after adjustment.