We will explain why you have to master the Chinese tones through two sentences. They would have the exact same pronunciation except different tones on shui and jiao.
xiǎo jie, shuǐ (the third tone) jiǎo (the third tone) yī wǎn duō shao qián?
Miss – how much is a bowl of dumplings?
xiǎo jie, shuì (the fourth tone) jiào (the fourth tone) yī wǎn duō shao qián?
Miss (prostitute) – how much is it to sleep with you (one night)?
水饺 – shuǐ jiǎo：dumplings
睡觉 – shuì jiào：sleep
小姐 (xiǎo jie) is used differently in parts of China. In Shanghai you can use xiǎo jie to call a female waitress & it’s understood to be waitress. However it is also used as slang to refer to prostitutes or bar girls. Therefore you probably do not want to randomly call a girl that who isn’t obviously a waitress or you might get slapped. If you want to be safe you can also address a waiter/waitress as 服务员(fúwùyuán).