Storage help please

How do you put items in cupboard or lockers I am new and trying to go on my first scavenging trip and need help

(D)rop them onto the tile. Note that (d) does drop things onto your feet, while (SHIFT+D) allows you to specify a direction to drop stuff.

You could also use the (/) advanced inventory to move stuff around and place it at a chosen place.

You can even quickly move stacks of things with , or M depending on what you want to do.
Check the (?) in various screens. You’ll find so many interesting features and potential good habits to pick up that way.