Evaluation > Notebook's Kernel (Mathematica Menu Item)

Notebook's Kernel specifies the kernel for a notebook.

File > New > Notebook (Mathematica Menu Item)

Notebook creates a new notebook.

Insert > Object... (Mathematica Menu Item)

Object opens a dialog to insert an embedded object, such as a bitmap image, spreadsheet, or document file, at the insertion point (Windows only).

Cell > Grouping > Open All Subgroups (Mathematica Menu Item)

Open All Subgroups opens all groups in a selection.

Cell > Grouping > Open/Close Group (Mathematica Menu Item)

Open/Close Group toggles a cell group between open and closed. Closing a group collapses all cells in the group so that only the head cell is visible.

File > Open... (Mathematica Menu Item)

Open opens a dialog box for opening an existing file.

[Right-click] > Open in New Window (Mathematica Menu Item)

Open in New Window opens the selected (or clicked upon) documentation link in a new help viewer window.

Cell > Cell Properties > Open (Mathematica Menu Item)

Open toggles a cell between open and closed.

Graphics > Operations (Mathematica Menu Item)

Operations opens a submenu to control grouping and graphic display placement.

Format > Option Inspector... (Mathematica Menu Item)

Option Inspector view and set all option values for cells, notebooks, and global preferences.