Menus are OFF by default toggle holotape to turn the clutter on! You can craft the holotape at the Chem bench Utility menu (recipe is hidden if you already have a holotape in your pipboy).
Clutter snaps to walls which is a side effect of using a snap point designed to prevent clutter on bottom shelves from trying to build on the ground
If you have stacked shelving units on top of one another you will have difficulty snapping clutter in the spot between the two shelving units. Similarly if you have multiple lockers snapped side by side you may have difficulty snapping clutter to some of the spots, they prefer to alternate. Use of Place Everywhere or Place Anywhere is recommended for the difficult spots.