It's a regular automatic transmission, so for almost all your driving you would want to use D5. D4 will lock out the tallest overdrive and is used for hilly terrain to keep the transmission from shifting excessively. D1-D3 are for holding lower gears only--usually only used for engine braking down a steep hill, crawling over steep terrain or when you are stuck in snow/mud. If you need D1-D3 you probably shouldn't be where you are with a car.
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