The top toolbar contains the most common and frequently-used buttons and tools. From left to right, you will see:
Left: "Back" button, Main menu and Project name.
Middle: "Connect mode", "Add sub-artboard", "Pen", "Undo", "Redo", "Group" and "Ungroup".
Right: "Artboard list", "State panel", "Zoom", "Publish", "Members", "Download offline prototype presentation package", "Preview" and "Enter full screen".