I'll answer your second and most important question first. In every dictionary (printed or online) there is a guide to pronunciation and a guide to the symbols used to indicate various things about each entry. One is a symbol that shows where the stress of the word is to be placed. These symbols are not (yet) standardized among all dictionaries but if you read the instructions on how to use your dictionary, the stress symbol ill be shown and explained.
You can hear and see an example using your word "address" here: Address | Define Address at Dictionary.com. This dictionary uses bold type to indicate the syllable of stress (n. uh-dres, ad-res; v. uh-dres]). Please note that your example has different pronunciations which give the word completely different meanings. But, they also offer the IPA designation of how to pronounce a word (address: n. əˈdrɛs, ˈędrɛs; v. əˈdrɛs). This small symbol - ˈ - placed before the syllable indicates that it is the syllable of stress.
As for your first question, it is only by years of use and experience that you might be able to correctly divide a word into syllables. Personally, if I have this task to perform, I always have my dictionary next to me. That's the only way I feel safe in answering such questions.
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