Interface
Side Bars
The tabs on the right side of an editor: open, close and resize them.
Some editors have a Sidebar at the right side. It can be resized by dragging. It can be closed and opened.
Opening and closing by menu and hotkey
The view menu provides you with menus to close and to open the Tool shelf.
It also shows the hotkey.
Resize
You can grab the border and drag the Sidebar to the left or to the right to expand or to close it.
Open Sidebar by Plus Button
When a sidebar is closed then you will see a little plus button. When you click at this button then the sidebar will reappear.