If an english word is spelled out in Katakana, does that mean its not a real japanese word? I'm asking this because my friend gets insulted every time I write an english word written in Katakana, so is it wrong? Or does it just have a different meaning?

Hello! I'm new (´；ω；`) Hello! I'm learning Japanese (I'm also new lol) and I have a question for anyone who knows Japanese and English- what is the best way to learn Kanji? I've been learning radicals, but I wanna know if there's a better way. Thank you~! (づ｡◕‿‿◕｡)づ