*Note -- If you put in control joints prior to pouring the slab, you don't need to use the groover. Groovy!
So why groove at all, if it just gets covered up? Well, the slab will be subjected all kinds of forces over its lifespan. The grooves provide the concrete slab with a vertical plane to crack, if it must. To be effective, the groove should be 1/4 of the slab's thickness in depth.
It's Time to Float and Trowel your Concrete Slab
How much pressure should you apply with the float? In this step is where concrete finishing becomes an art, like taping and floating drywall. It depends on the hardness of the concrete slab at this point. If you've never done this before, just start off with a light touch and get the feel of it -- it's all a matter of experience.
Next, it's time to begin to trowel the slab using your steel trowel. Think of this step as like floating, except that its objective is to take the concrete slab to more precise levels of smoothness. Further successive passes yield more precise results.
Some applications don't want or need any further smoothing of the surface. When would this be? Sidewalks fall in this category. If you're planning on laying ceramic tile on the slab using mortar, a super-slick surface isn't needed. Also, don't smooth too much any time a non-slip surface is called for. You can give it a broom finish at this point.
Trowel it the first time, and if a smoother surface is desired, let it dry out more, and then trowel it another time. Generally speaking, three passes will yield the best results. Beyond this, you won't notice any improvement.
Finally, let the concrete slab dry completely, and then remove the form and discard the lumber.