我会说一点儿。

Put it right after someone asks if you speak Chinese. You can use it as a full sentence. It is like a verbal shield. It sets expectations low so people don't start speaking at 100mph. Just say it with a smile. Most people will be impressed you even know this much!

Use it at a restaurant when the waiter looks hopeful. Use it when meeting your partner's parents for the first time. It is perfect for taxi drivers who want to chat. It works in business meetings to show you are trying. Basically, use it whenever you want to be polite but cautious.

Don't use it if you are actually fluent. That feels like a weird humble-brag. Also, avoid it in high-stakes legal or medical situations. You don't want a doctor thinking "a little" is enough for surgery instructions! If you know zero Chinese, just say 不会 instead of this.

Chinese culture values humility deeply. Even people who are quite good might still say 一点儿. It is a way to stay modest and avoid "losing face" if they make a mistake later. By saying this, you are actually acting very "Chinese" already. It is a social lubricant that makes everyone feel more comfortable.

You can drop the 儿 sound if you are in Southern China. They just say 一点. You can also add 中文 (Chinese language) to be specific: 我会说一点儿中文. If you want to sound even more modest, try 一点点. It sounds a bit cuter and even more diminutive. It’s like saying "just a tiny, tiny bit."