Bringing back a window you closed by mistake
Sooner or later a panel disappears. The window is not lost, it is just hidden, and it comes back in two clicks.
Reopen a panel
Open the view menu and choose the panel you are missing from the list of tool windows. It reappears, usually docked to the side.
Dock it where it belongs
Drag the panel title bar toward an edge of the main window. Guide markers appear. Drop the panel on a marker to dock it, or in the centre to leave it floating.
When it is truly a mess. The editor can reset the window layout back to its default arrangement. Do that rather than dragging for ten minutes.
With the workspace restored, return to the solution explorer and carry on. If you are moving work to a new project, the next lesson on moving files between projects covers it.