Blender’s Layer System
If, as a first-time Blender user, you rush to try to move your object around by attempting to use M as a hotkey, you may be surprised when Blender presents you with a funky pop-up panel of 20 unlabeled buttons. Interestingly, the M hotkey does activate a move function, but not like you’d expect. It allows you to move your object to one or more layers.
Each button in the pop-up panel represents a single Blender layer. Left-click a button, and your selected object moves to that layer.
Blender’s layer system is pretty unique among computer graphics software; the layers aren’t layers in the traditional sense, where they’re arranged in a stack and objects can live in only one layer at a time. Instead, Blender has exactly 20 layers and objects can simultaneously live on multiple layers. As a result, Blender layers tend to be treated as a quick way of grouping objects.
You can control which layers are visible by using the block of layer buttons in the 3D View’s header. You can tell if a layer has objects in it at a glance by checking to see if the layer button has an orange circle within it. Shift+left-click a layer button to toggle its visibility. Left-clicking Shift+any layer button makes that layer visible and all others hidden. Pressing the Tilde (~) key makes all layers visible.
A neat feature allows you to arbitrarily enable or disable multiple layers at once, both in the 3D View’s header and when moving an object between layers. If you Shift+left-click a layer button to enable or disable it, keep your mouse button pressed; you can drag your mouse cursor around the layer buttons, enabling whichever layers your cursor floats over. This also works in other parts of Blender’s interface. Although this feature is most useful in layers, you can use it for check boxes, toggles, and radio buttons, too.