Rice is a type of grain that quickly multiplies in size when cooked, so measuring the amount is very important, If you use too much water then your just making soggy rice and no one wants soggy rice. So measure rice in cups (not drinking cups) and water amount appropriate to the rice, the cooking pot normally has lines indicating water level, the amount of rice you put in depends on how much you want to eat or can eat, but be careful rice expand quite a lot so be aware of that.
Here's a Chart with Water to Rice Ratio:
Store bought rice grain normally contain excessive starch and that doesn't taste so good when cook so make sure to rinse. Nothing complicated just submerge the measured rice in water and and mix it around a bit at this point you’ll see the water become murky or cloudy so drain the water and repeat 2-3 times… you know what they say 3 times a charm. After rinsing just fill cooking pot with ratioed water (Make sure ya rinse because sometime rice grains, this process not only does it wash off startch it also allows the rice to absorb the water better)