The center rail should have four slots for the four strings to feed thru. They lay in the open and hard to manage untill you slide the upper or lower section back into place. I use 50' of string (really) when stringing. I work the strings back and forth thru the slot (sometimes several times during the process) untill I have slid all sections of the shade back together again. Additionally, I use a three inch thredding needle to help in the stringing process. Their is/was a link in this forum for this process, too. I will try my pix for you.
Don & Dona W/yorkies Gizmo, Master Chief, & Tali
2011 Flagstaff 8528 BHSS 2015 Ford 6.7 XLT
2010 Full Timers & Still Going