Building the Windmill Structure
Windmills are your entry point to mechanical automation. Start by crafting the windmill block and placing it in an open area with good wind exposure—avoid dense forests or enclosed spaces, as wind strength varies by location.
Once placed, the windmill will begin generating rotational power through its sails. You can see the rotation visually as the sails spin. The faster the wind, the more power it generates.
Connecting to Your Machines
Attach an 
axle to the windmill's output face. Axles transfer the rotational energy horizontally or vertically to adjacent blocks. Chain multiple axles together to reach your processing machines like millstones or saws.
If you need to change direction or step up power, insert a gearbox between axles. Gearboxes allow you to redirect energy flow and adjust torque output for different machinery needs.
Testing Your Setup
Place a simple machine like a millstone next to your axle network. Feed it grain or other compatible materials. If the axle is spinning and the millstone is receiving power, your windmill is working. You can now expand by adding more machines or building a second windmill for increased output.