Add/Modify Comment... or Remove Comment.

Insert a mathematical function. See the section Formulae for more details.

Insert a series. See the section Series for more details.

Insert a link into the selected cell. See the section Link Cells for more details.

Insert a special character into the selected cell.

Embed another KOffice document into the sheet.

Insert a chart. See the section Inserting a Chart for more details.

Opens the standard KDE file dialog to insert a picture.

Insert data From Database..., From Text File... or From Clipboard.... See the section Inserting External Data for more details.