Install the front (side with the core) and bottom struts first. Tighten them up to the desired amount, then install the rear strut last. I use a 5/16 open end wrench for the front and bottom nuts (don’t use the box end, you won’t be able to remove it once the screws are fully threaded in).
The rear strut has captured nuts, . You should be able to reach a finger between the strut and the top rail (or between the rear strut and bottom strut( to press and hold the nut in the recess.
There are some printed nut holders (made by @bitingmidge some time ago). Here’s the link