What's the difference between "isn't" and "ain't" ? When I should use "isn't" and when I should use "ain't" ?

Writing about me Hi. I will write about me because it is the only subject that I really know, I guess. I am a 26 years old brazilian guy that lives in a small city next to Porto Alegre. I like to play video games, practice muay thai and mainly listening to music. I work at a IT company as software developer, but my real goal is work creating games. I was graduated in Game Development in a local college. I am very excited with the idea to move to Ireland, thats actually it is a better place to live and work with IT. Would be great to meet some irish people here to practice with a real person and with the irish accent. Please, feel free to correct my text and suggest more natural phrases. Thank you.