Many times the word's mishkal or binyan (i hope you are familiar with those linguistic structures) tells you where to put the stress. But sometimes you just can't tell just from looking at word how to stress it (e.g. בוקר = morning, when the first syllable is stressed, or a cowboy, when the second is stressed). In this case, context is crucial.

OK. For example, the stress of the word אוכל ('ochel, food) is on the first syllable, and the stress of the word אוכל (o'chel, to eat) is on the second syllable. Their spelling is the same, but their stresses are different, which leads to difference in their meanings. Now how do we know the stress of all these Hebrew words?

I didn't understand your question :\