How to append the Asset into your scene
To use this Asset, just go into the destination project and click on "File" > "Append" , then navigate to the file you downloaded and append the Group (not the Object!) with the name "Asset_suspension_bridge".
How to change the length of the bridge
You can use the little cube next to the first element of the bridge to change the length of the array. Just grab and move it along the Z-axis.
If you have other problems, feel free to contact me via my blendermarket page!