Distinguishing between Blender’s Object Mode and Edit Mode
As its name indicates, Object mode is where you work with whole objects. However, Object mode isn’t very useful for actually changing the internal structure of your object. For example, select (right-click) the cube in the default scene.
You know that you can turn it into a more rectangular shape by scaling it along one of the axes. But what if you want to turn the cube into a pyramid? You need to modify the actual components that make up the cube. These changes are made by entering Edit mode.
You can get to Edit mode in one of two ways: with the mouse or with a hotkey (or, if you have the Pie Menus add-on enabled, both!). To use the mouse method, left-click the Object Mode button in the 3D View’s header. From the pop-up menu that appears, select Edit Mode.
Be aware that if you’re working with an object other than a mesh, such as an armature, the contents of this menu may vary slightly to relate more to that object. However, with the exception of Empties, Lights, Cameras, and Speakers, all objects have an Edit mode.
Of course, Blender also has a hotkey to enter Edit mode. Actually, technically speaking, the hotkey toggles you between Object mode and Edit mode. Pressing Tab is the preferred way to switch between modes in Blender, and it’s used so frequently that Blender users often use Tab as a verb and say they’re tabbing into Edit mode or Object mode. This language is something you come across fairly often in Blender user forums and in some of Blender’s online documentation.
If you have the Pie Menus add-on enabled, pressing Tab no longer toggles between Object mode and Edit mode. Instead, it brings up a pie menu with the option of many modes. It isn’t quite as fast as toggling with Tab, but it can be pretty fast if you use the hold hotkey, drag mouse cursor, release hotkey method of using the pie menu (plus you get the added benefit of easily choosing other modes).