I'd like to know what the difference between 悪 and 惡 is. And also what usage you should do between both. I heard that they both mean "bad"
惡 is the traditional (pre-1946) form of the kanji, while 悪 is the new, simplified form. The simplification in this case may not seem much (just a single stroke has been removed), but it was probably made to make the form of the kanji more 'natural' and flowing.
惡 is 旧字体 of 悪. Recently 惡 almost always is used for cool-looking designs in manga, anime, and so on.