Gather your spring tighteners, 4 finish nails, bow limbs, springs and a 60" length of para-cord casing (pulled off the springs in previous step).
There are notes on the pictures below for reference. Attaching the limbs
Thread one of the spring tighteners into the loop of strings. Use the threading string on the other end of the spring to pull the spring through the bottom hole. Now put the wide end of one limb through the center of the spring loop. Now thread the spring loops through the top hole. Thread the top spring tightener through the loops sticking up from the top hole. Now lay the crossbow face down with the limb pointing toward you. See picture for correct layout. Now it is time to tighten the springs to hold the limb in place. Holding one tightener in each hand, turn them both 2 full rotations toward yourself at the same time. Stick finish nails in the holes drilled for this purpose to hold the tighteners in place.
Repeat with other limb.
Attaching the string to the limbs
Take the 60" length of para-cord casing and the 2 loose ends together to make a loop. Now tie the knotted end to one arm using whatever kind of knot you are comfortable with. Be sure to leave a loop about 3/4" to 1" to loop around end of the arm. This ensures string is secure. Twist the loop of casing to make a nice tight string between the limbs and tie to other limb the same as the first. You may have to adjust the length of the casing or the amount of twists to get a tight fit.