Managing an automatic is a little different from using a standard transmission. The automatic does not have the safety feature of parking in gear.
Off-road an automatic needs special attention. During crawl action as well as when you get going.
When you get going again you have to follow this procedure: Foot on the main brake, start engine, put lever in "N", release emergency brake, shift into "D" - or more likely when in a severe off-road setting, into "1" or reverse.