your drain hose/pump are probably clogged. Start by pulling the impeller offer (some of the top nuts are reverse thread) , then remove all the plastic pieces you can SLOWLY without breaking them. Every brand is VERY easy to break !
Pull out whatever screen is in your way to access the "chopper" blade. Check to make sure this is not bound. Clean out ANY garbage in the sump that you find. Run it.... still not draining correctly? Go to the disposal/sink. Pull the hose off and look for BOOGERS. See if you can blow through it. (even though there is a check valve you should stil be able to blow a SMALL ammount).
Free? If not you probably have a clogged hose. Pull the dishwasher out and pull the drain hose off to check for obstruction.