Lay a pair of 2 by 4 boards and several spindles across a pair of saw horses. Lay two plywood boards across the spindles and 2 by 4 boards. Clamp a 2 by 4 board on the edge of the plywood to secure it in place.
At one end, clamp a spindle to both pieces of the plywood.
Clamp another spindle to the front of the plywood.
Carefully lay out the two pieces of plywood so the distance between the 2 by 4 and the clamped blocks is the dimension for the overall height of the railing section.
Cut a pair of 2 by 4 boards to the length you require and place them against the wood blocks on the edges.
Lay down a pair of gauge blocks to establish the position of the first wood spindle. Secure the wood spindles in place with screws.
Position the remaining spindles in place and secure them with screws. Repeat this until you have about ten to fifteen spindles in place.