Use the Line object in the Drawing toolbar to make the L shape
Remember that holding SHIFT helps gets line parallel to cell grid
Make sure the ends all align
Click one line; hold CTRL and click each line in turn; use left mouse button
to open popup menu and use Group
To move L shape let mouse pointer hover over a handle (open circle) until
you see a four-headed pointer; if pointer is double-headed and you drag then
you will resize the shape
best wishes