Setting Panel Width
In between of left and right panels is the Split bar. If you want to know how the Split bar looks like, see a screenshot with description in chapter Main Window Components. You can change position of the Split bar to enlarge one panel at the expense of other panel.
You can change position of the Split bar using mouse drag. To start it press (and hold) left mouse button on the Split bar. The Split bar has also right-click context menu with percentage proportions of left and right panel widths (20/80, ..., 50/50, ..., 80/20). To set panel widths to be equal use mouse double-click on the Split bar.