Choose a change, choose a direction, and run it. The gas moves along one curve and the curve stays on the P-V diagram, so pressing several in turn builds a picture you can compare.
The area under a curve is the work the gas does. Expanding sweeps out a positive area, compressing a negative one, and an isochoric change sweeps out none at all because the volume never moves.
The three bars are the first law, Q ＝ ΔU ＋ W. An isothermal change keeps the internal energy fixed, so every joule of heat becomes work. An adiabatic change takes no heat, so the work has to come out of the internal energy and the gas cools as it expands.
The panel names at the top right open and close each panel. Drag a panel by its header to move it: panels snap to each other and to the screen edge, and a panel resting on an edge drops the rounded corner on that side. Double-click a panel title to switch between floating panels and a single fixed panel at the top right. Pick a row in the condition panel and its value appears in the child panel beside it, which follows the parent as it moves.