2K Furniture Designs 813 Instruction Manual page 6

Step 3, use bolt # 3, nut # 6 to assemble Part 【 A 】 to Part 【 B 】 and Part 【 E 】, See detail 3;
Then use bolt # 1, washer #4 and nut #5 assemble Part 【 D 】to Part 【 B 】 and Part 【 E 】, see detail 4;
Repeat to assemble the other half of bed.