For me, the whole point of a rice cooker is that it's easy and forgiving to use. It probably helps that we have rice almost every day, so we get lots of practice.
As others have mentioned, you have to rince your rice - for white rice I rinse it at least twice, more if I don't think the water is clear enough. Additional rinsing does make the rice less sticky, but it takes longer.
For adding water, I'm a bit less accurate than the other people who've answered. We rarely make "a cup of rice," we just pour in as thick a layer in the cooker as we think we'll need. If we want leftover to fry the next day or if we have a dish with a lot of sauce, we'll do more. "A small amount" is a layer about a cm deep in the cooker, a "larger amount" is a bit more than 2 cm, and "a lot" is probably 4 or 5 cm deep. After rinsing and draining most of the rinse water, fill the cooker until the water is a bit less than twice as deep as the rice. i.e. if you put in a cm of rice, the water should be a 2cm deep. Once you get to about an inch of rice, the water can be a bit less, so not quite 2 inches.
For brown rice, I put in about an extra cm of water.
If it were me, and my rice cooker didn't just work, I'd assume it was busted and get a new one. We have one that just has a single button that you push down to start the cooking cycle, and it takes about 1/2 hour to cook an inch of white rice. We also have a newer cooker than has both a Normal and a Fast setting, the Fast setting would take about 20 minutes to do the same amount.