This project covers installing the deck railing.
Measure and mark the proper space between the bottom rail and the deck (check local building codes). Position the bottom rail; drive two nails or screws into each post. Install the top rails, top edges flush with the post tops. Drive two 3-inch fasteners where rails join at the corner.
Use a jig like this to space and plumb balusters and position them at the right height. Check for plumb at every fifth baluster. Make incremental adjustments in the next few balusters as needed. Attach each baluster with one 3-inch screw or nail driven into the top and bottom rails.
At a corner make a precise miter joint where two pieces of cap rail meet. First, on one of the boards, cut the mitered end only, and let the other end run wild. Check the fit of the miter. If the fit is good, cut the other end of the cap rail. Drill pilot holes and drive screws to draw the joint tight.