The Toolbar panel, like in most applications, is a group of commands providing quick access to commonly used tools and operations.
Saves the current level.
Allows you to connect to or assign your Source Control solution.
Opens the Content Browser displaying all of the content assets contained in your game. This is where you go to create, import, and edit all content.
Opens the Unreal Engine Launcher to the Marketplace section.
Displays the Settings menu providing easy access to commonly used options controlling selection, editing, and previewing aspects of the Level Editor.
Provides access to create or edit any Blueprints in the world, including opening the Level Blueprint for the current level in the Blueprint Editor. This menu give you quick access to setting up the framework for your game - game rules, player type, HUD, etc. - from within the editor.
Enables you to create a new Matinee sequence or edit any existing Matinee sequences in the level.
Performs a the build operation on all levels (persistent and streaming) open in the editor. Building precalculates as much data as possible relating to various aspects of the level. For instance, static lighting - lightmaps, shadows, global illumination - and geometry are calculated during this process. Clicking the arrow displays the Build Options menu.
Starts the game in normal play mode. Clicking the arrow displays the Play Options menu. See the Play In Editor section for more information.
Launches the current map on any of the supported platforms. Connected devices are listed in the menu accessed by clicking the arrow.