A fresno trowel is a long-handled steel trowel and should be used just like a hand-held steel trowel. Always float the concrete before using a fresno.
Keep float blades as flat as possible to avoid sealing the top surface. Sealing the surface can trap escaping bleedwater and air bubbles directly below surface, which can cause blisters and delaminations.
Similar to floating, keep the trowel blade flat as possible for initial troweling. As the concrete hardens, progressively increase the angle of the trowel blade to increase the pressure on the surface of the concrete.
As the concrete becomes harder, switch to a smaller trowel (right hand) and continue increasing the blade angle to increase blade pressure to create a smooth and hard surface. In this image, you can see the larger trowel in the finisher’s left hand.