Once you have the spoke threaded on to the hub eyelet with the proper crossing, you can use the flat head screw driver to reattach the spoke nipple to the top of the spoke

Match up the spoke to the hole and place the nipple on it. Begin to attach the nipple and spoke with the flat head screw driver

The screw driver won't be able to tighten it completely so that is when you need to use your spoke wrench to finish tightening the spoke