Round trampolines aren't that expensive, especially if you buy one used. Now you have all the parts out on the lawn, but there are so many pieces that it's starting to look impossible. Hopefully your trampoline came with an instruction manual, but even if you dont, these steps will give you the basics to make this job easier. Just remember when assembling that the hardest part is putting on the springs. No tools are necessary. Make sure to have a pair of young, strong arms to help you out.
Pick the area in which you will be setting up your trampoline. Lay out all the pieces of the frame in a circle. In a basic 14-foot diameter trampoline, the pieces will be: 4 top rail sections (which look like curved metal), 4 top rail with leg sections (curved metal with two short tubes aiming down at either end), 4 leg bases (which look like the letter "W"), and 8 vertical leg extensions (which look like straight metal poles).
Take each leg base and attach the vertical leg extensions on each end of the "W." When the leg base has the vertical leg extension attached on each side, the whole unit is now called the support assembly. Have your helper hold the support assembly upright like a "W" while you attach two top rails with the leg sockets, one on the top of each side of your "W." You'll have an upright "W" with two top rails sticking horizontally off each end, forming the top beginning of your circle. Continue making the circle by adding another "W" support assembly and top rail section all the way around the circle until the circle is complete, and free-standing. There will be gaps across the top of each "W." This is where you need to get your 4 remaining plain metal top rails and slide them into place, completing the frame's circle.
Lay the trampoline jumping mat in the center of your circle. Take a spring and hook it into a "V" ring on the mat. Hook the other end of the spring into a hole on the top frame rail. There are 96 "V" rings and holes. Count 24 holes from your starting hole and attach a spring there. Count another 24 holes and attach another spring. Repeat until you have 4 strings attached at even intervals. This helps equal the tension on the mat and makes attaching the rest of the springs easier.
Split the distance between each spring, and attach the next four springs. Continue splitting the difference between each spring in this manner until all the springs are attached. Make sure you count each hole as you attach springs (counting and matching up your "V" rings and holes evenly and correctly), otherwise you'll end up having to wrestle the very tight springs off later to align them, which is not fun.
Attach any frame pad that may have come with the trampoline by assembling it over the springs. Straps will be hanging down that can be tied or Velcroed to the top frame rail. Hang your ladder from the top rail in the area you choose for getting on and off the trampoline.