Or, humans can't live on bread and water alone, and neither can plants...
I have some friends who swear up and down that they have a brown thumb. Every plant they take in dies a long, slow, horrible death. Sometimes it's because they forget to water enough (and even more rarely, too much). Usually when I ask them what happens, they say they don't know.
tl;dr- Buy a good liquid plant food and add it to your plant water as directed. Sometimes you need to re-pot your plants in new soil. Ask at your local garden centre what they suggest. Sometimes your plant has outgrown its pot and needs a slightly bigger one, but if you don't give food to your plant it will likely never get to this point.
If you actually want to learn something about it, read on...