A stressed syllable is the part of the word that gives you most emphasis. Example: Sofa Telephone Award you can say wich syllable is stressed by saying aloud the word and seeing wich syllable make sense.
Lets make a few examples: Sofa doesnt sound right but sofa does. Telephone sounds right but telephone doesnt sound right. You can do the same excersise to know which syllable is the stressed one. But be careful some word same good either way like: Detail and detail. so dont worry if you cant find the syllable stress of some words.
all one syllable words have stress on the one syllable. Example: Eat Drink Sign Well School Glass can
Also the stress syllable can change depending on how it is use in a sentence. ď‚ž You like soda, emphasizes that you like soda no other one. ď‚ž you like soda, emphasizes that you really like soda not someone else. ď‚ž You like soda, emphasizes that you like soda not cofee or milk.