It's supposed to look like a cute emoji that should be used to respond to something cute. Furries and people who like anime use it. There have been so many memes of furries using it excessively in role-play with strangers that the word is viewed as cringey by many people. If you unironically say this to somebody who is not a furry or anime fan, don't expect a positive response. Not many people like it. Don't use this word or owo when trying to flirt with somebody you just met online (or in real life; if you use it in real life, you sound stupid), because there is a chance they won't like you and will just think you're annoying.
Situations you should not use uwu in.
Messaging a stranger whom you found attractive online. If they are a furry, you can use the word uwu, but don't use it if you are unsure if they are okay with it or not.
You: "Hey, I just looked at your photos here on Tinder. You're fineee asf. uwu"
Somebody: "Ummm...I'm not sure how I feel about that word..."
You: "What?"
Somebody: "I'm not a furry."
You: "Oh...okay. uwu s-sorry!"
Somebody: "I'm going to have to block you. You're making me feel uncomfortable. A relationship between us will not work out."
Messaging your boyfriend/girlfriend when asking for something. If they aren't a furry or don't use uwu, it's best to not use it.
You: "Hey, send nudes uwu"
Them: "Nah."
You: "Why? uwu"
Them: "Because you used uwu unironically."
You: ":("
Them: "Sorry. You should know to not use uwu when asking for nudes from somebody who isn't a furry. I've never even used that word."
Here are some situations in which it is okay to use uwu
When messaging a furry who likes roleplay
You: "*nuzzles you* uwu!"
Them: "*pets you* uwu!"