If the defaults don't quite give you what you want, you can adjust each of the settings individually. This page explains how each setting works.
Setting 1 - Detail
AutoHDR is different from other HDR solutions in that it performs a complex mapping of the image so that it can correctly adjust every pixel without creating halos and other visual artefacts. In simple terms, this involves dividing the picture up into small pieces and adjusting the highlights and shadows for each piece individually. Increasing the level of detail will divide the picture up into smaller pieces (*1). When the highlights and shadows are adjusted for each piece, having smaller pieces produces a sharper image with more fine detail.
Detail can be set from 0 to 10 with the following results:*1 This is a good way of thinking about it but in reality it's much more complicated.
Setting 2 - Contrast
Contrast affects how far dark areas are pushed towards black and how far light areas are pushed towards white. AutoHDR applies this to each individual piece of the image rather than globally so that colour and local detail can be retained.
Contrast can be set from 0 to 10 with the following results:
Setting 3 - Saturation
Saturation affects the strength of colours. AutoHDR manages the relationship between hue(colour), saturation and lightness to keep colours looking 'right'.
Saturation can be set from 0 to 10 with the following results:
Settings 4&5 - Shadows and Highlights
When AutoHDR maps the shadows and highlights it is working out which pixels need to be lighter and which need to be darker based on their surroundings. In the representation below, the red areas need to be darkened and the green areas need to be lightened. The 'Shadows' and 'Highlights' settings simply independently adjust how much each of these effects is applied.
Next: Advanced Settings