The first section deals with the usual monitor-related settings
Warhammer III supports fullscreen and windowed. Windowed actually means borderless, but the window positioning isn't perfect, so some parts of the window are cut off, making this mode unusable.
The details setting presets are "Ultra," "High," "Medium," and "Low". The next page has a comparison between those.
Available anti-aliasing modes are "Off," "FXAA," "TAA," and "TAA High."
There's a big list of additional settings options to further fine-tune performance.
Unlimited video memory lets the game allocate more memory than what it thinks is reasonable. Considering the game properly detects the VRAM size, enabling this doesn't seem necessary.
V-Sync can be turned off as there is no hidden FPS cap.
Resolution Scale lets you upscale the rendered image for higher FPS. Only upscaling is possible; the range is 50% to 100%.