Typically the covered detergent compartment is for "regular" washes. The first cycle is a pre-rinse and then the compartment opens to release the detergent for the wash cycle. The open detergent compartment is for adding extra detergent if you have especially soiled dishes.

Usually there's some kind of fill line or you can check the owners manual for the suggested amount of detergent. Or you can use on of the many little packets/tablets and eliminate all the measuring.

I bought a Sears Kenmore with the same configuration. Apparently if you use pwder gel or liquid DW detergent, you fill both. I had a question, called both the manufacturer (Sears) and the makers of Cascade. I had those solid tablets. Which section should I put the tablet in? Both told me to put it in the larger or main section.

jannie;

If you purchase the tablets or packets, they will go into the main, covered compartment.

If anyone is like me, who has a dishwasher with small, twin compartments(4 total), just sit the tablet or packet on the floor of the dishwasher before the main wash starts.