Hi Newb-person. I'm Patty. I've three characters here.
This is Marlene McKinnon. She'll be Order eventually but at the moment she's a sixth year pureblood Slytherin who is wrestling internally with the fact that she doesn't think muggles and muggleborns are as bad as she originally thought thanks to her sister secretly dating a muggle. That's rather on the down low for now. But she's been reaching out more to non-purists lately. They might get along? Or at least maybe get along in the future.
Li Shen is a fifth year Gryffindor. She's a sweet girl who loves ghosts. I can't see them really knowing each other directly, but she'd be nice should she run into him.
Professor Walter Morris is professor of astronomy. He's a nice enough professor that puts a lot on respect. If you are disrespectful, he will call you out on it and he doesn't tolerate disruptions in his class. So Morris' opinion of him will be mostly based on his classroom behavior.