Rhythm in phonetics is the speed and cadence of how you say a sentence. Some beginner students might say - each - word - in - a - sentence - at - the - same - speed and sound a little like a robot. Developing different speeds and knowing when to slow down and speed up can give your spoken English more interest.
Intonation is considered the ‘music’ of the language. Questions can be asked with a rising intonation, where the pitch goes up. This might be a genuine question to which you don’t know the answer. For example, ‘John’s still on holiday?’ said with a rising pitch means the statement is a question which needs answering. If the phrase is said without a rising intonation, it’s information that you already know and may just need confirmation on. Intonation can also show emotions like surprise.
Stress is saying a syllable or part of a word more strongly and can be at word level. For example, RECord is the noun of an athletics world record perhaps, whilst reCORD is what you do to a song when you copy it onto a CD.
Stress is also important at sentence level where the meaning can be changed depending on which whole word you stress. Below is an example of how the meaning of a phrase is changed when the words underlined are stressed.
I thought your brother was a bus conductor.
[You thought that someone else thought he was a bus conductor].
I thought your brother was a bus conductor.
[You thought I knew he was a bus conductor].
I thought your brother was a bus conductor. [Not your friend’s brother].
I thought your brother was a bus conductor. [Not your sister].
I thought your brother was a bus conductor.
[I didn’t know he still is a bus conductor].
I thought your brother was a bus conductor.
[Before, I thought he was an orchestral conductor].
I thought your brother was a bus conductor. [Not a bus driver].
The implied meaning of this short sentence can be changed seven times depending on which word is stressed!
Source: https://www.nordangliaeducation.com/biss-puxi/news/2022/02/22/stress-rhythm-intonation-phonology