When you open the box, you will find set of glides, before you assemble the glides you need to separate glides. For example, how to separate the Left glides:
There are I1 and J1. You should undraw the J1, at the same time, you will find a black plastic at the end . You should hold the plastic and drive up it (If separating the right glides please hold the plastic and drive down it), then undraw outside, you will find glides had been separated. Following the instruction, you will found the production is assembled easily.