The wooden crate that you can make and drop on the ground is different from the crates you see that are placed on the ground like walls, or chairs etc. To make the placeable wooden crate that can be stacked, have hammer, nails and planks in your inventory, then right click on the ground near you where you would like to place the crate. When the menu pops up, there is the option "walk to" and "Build" the build menu is where you want to find "Wooden crate" Once you build one, you can do the same action to build another, but press the "R" key, and it changes the height of the crate, so it allows you to place it on top of other crates. Thak you you save my life and stop me in making hundreds of useless wooden crates!