stonedeaf, not to avoid answering your questions, but it sounds like you might want to get in contact with someone familiar with the hobby. Maybe your Local Hobby Store (LHS), or a local club that can provide direction. However, for your answers, to your questions.

The screw on the servo is for holding the servo arm in place. There are holes in the arm for inserting your pushrods using either a 90 degree bend and a quick connector to hold it in place, or you can place a "z" bend in the rod and wouldn't need a connector. On the other end of the rod, you screw on clevis's which attach to the control horn. The mechanical adjustments that are indicated are done by moving the clevis back and forth until you get the control surface as close to the neutral position as possible. The rest of the adjustment is done via the radio using the 'sub trims' and the 'servo travel' settings.

As far as attaching the hinges to the wings and stab, you use the ca hinges supplied in the ARF. By inserting them in the wing and then in the aelerons and making sure you have only a small gap between the wing or stab, and the control surface, you then drip in CA glue. The glue will then run along the ca hinge into the wood and spread out allowing for an area of glue that attaches the hinge to the wood.

This is pretty general and does not contain the total detail needed to put all of this together. If you do have the ARF and the instructions for the Avistar they do have much of the steps outlined. As indicated though, you might seek local help that can show you or demonstrate the techniques, or walk you through building your ARF.