Structure menu
Add — Select something from the submenu to create a new item in the outline.
Move — Move the selected item spatially, while trying to preserve existing structure. The thing to look out for here is that Move Left and Outdent are subtly different: while Outdent leaves the item where it was vertically, possibly turning some of its siblings into its children, Move Left gets the item out of whatever group it's in while not affecting its siblings at all.
Indent — Move the selected item to the right, turning it into a child of the item before it in the outline.
Outdent — Move the selected item to the left, making it a sibling of what was its parent. This turns any of its siblings that came after it in the group into its children.
Group — Put all selected items into a newly created group.
Ungroup — Remove the selected group and leave all of its children at the level of the parent.
Split Task — Divides a task into two tasks, so you can push some of the work off to a later date.
Connect Tasks — Choose a type of dependency line for relating two or more selected tasks.
Disconnect Tasks — Remove dependency lines from between two or more selected tasks.
Assign Resource — Choose a resource to assign to the selected tasks.
Clear Assignments — Remove all resource assignments from the selected task.
Sort Selected/All Tasks/Resources — Reorder the selected items (or all items, if none are selected) based on the values in some visible column. This is an on-demand thing, not a permanent auto-reordering mode that you turn on.