Here's an example. Look at this dictionary page for the word 'computer': https://www.oxfordlearnersdictionaries.com/definition/english/computer?q=computer Click on the audio icons: there is one for American English and one for British English. You'll hear this word being said in two accents, but in both cases you'll hear that there are three syllables: COM+PU+TER. You'll hear that the second syllable - PU - is longer and said with more force than the other two. You might also hear that there's a slight pause before the second syllable. Another very important thing to notice is that the vowel sounds in the two unstressed syllables (the first and the third) are very weak and 'neutral'. The 'o' and the 'e' in 'com' and 'er' don't sound like 'o' or 'e' when they appear in short words - because they are unstressed, they are just a brief, effortless sound like 'uh'. This is what we call a 'schwa', and you'll see it in dictionary pronunciation guides written as /ə/ Crudely transcribed, the actual pronunciation of 'computer' is something like this: cum-PEW-tuh (GB) or cum-PEW-tur (US) - a strong middle syllable with a weak syllable on either side. How do you know which is the stressed syllable without listening? Look at transcription next to the audio icons: /kəmˈpjuːtər/ Can you see the little mark like this ' before the p? This is what tells you that the following syllable is the stressed one: this is what tells you to put the emphasis on the 'pu' part of the word. I hope that's helpful.

The main stress is the syllable that we emphasize in pronunciation. For example, we say the word “pronunciation” has the stress on the second syllable and we say proNUNciation. Sometimes stress can change the meaning of a word. For example, there a lot of English words that depending on the stress it can be a noun or a verb. We see that in words like record vs. record. With the stress on REcord it is a noun but as reCORD it is a verb. They write these in most dictionaries under the spelling of the word with either capital letters like I did or with accent marks. Hope that helps!