Hello, I am having trouble writing an weird character. He's supposed to be kind of an odd and eccentric person, but I don't really know what that might look like.
Different “eccentric” characters are strange in different ways. A lot of it will depend on the world that he lives in.
Think of Luna Lovegood. Even in a world of magic, Luna was not afraid to believe in the unbelievable. She was far off and distant, and that was reflected in her appearance. She wore odd clothing, had unusually pale hair, and large blue eyes.
Also realize that part of a character being “eccentric” means they simply don’t think of what other people will think of them. So what’s really going on in their head? How does that translate into their actions and their appearance?