The phrase "Mmm" does not have any vowel within it. Then, how do I suppose to pronounce it? Also, are there other words that don't include any vowel in them?

Native speaker’s answer
Rebecca
That's right. It doesn't have a vowel! "Mmm" is an exclamation and sounds like a short humming sound. It's like saying the letter "m" but with your mouth closed the whole time! There's also "hmm" which is said when you're thinking about a solution or answer to something. There are other variations of "hmm" and "mm" to mean different things as well. And then there's "shh," which is said to tell someone to be quiet, and "psst," which is said to get someone's attention quietly. "Nth," meaning an unspecific number of something, "brr," which expresses being cold, and "pfft," to be dismissive of something. Ex: Mmm. This is so delicious. Ex: Hmm. I'm not sure how to answer that. Ex: Shh! You need to be quiet in the library. Ex: Psst. Come here! Ex: I'm watching this episode for the nth time. Ex: Brr, I'm so cold. Ex: Pfft! It was nothing.