If you don't know what spoilers are you have to learn English a little more xD.
But for beginners: Spoilers are often things that other people say to you that might spoil your anime experience. For example, when something big is going to happen to but you already know what is going to happen so it has a less impact. But it might be possible that you're spoiling it yourself by watching the last episode or lovey-dovey scenes for example xD or reading the light novels or manga where an anime is based on.
Definition from thefreedictionary.com:
A published piece of information that divulges a surprise, such as a plot twist in a movie.