Pronunciation is an important part of speaking a language well. It makes it easier for people, both native and non-native, to follow what you’re saying. One of the complications of pronunciation in particular is that many times the stress of the word changes the way vowels are pronounced. Take a look at the following words for example:
These two words can be both a noun and a verb. If you put the stress on the first syllable, it’s a noun. If, on the other hand, you put it on the second syllable, it’s a verb. The “o” in both of these words changes depending on whether the stress is on the first or second syllable. If the “o” is unstressed, it turns into a schwa, the most common vowel sound in English. It is important to remember that in addition to putting the stress on the other syllable, you must also pronounce the “o” like a schwa to reflect that change in stress. Otherwise, a native speaker isn’t 100% sure if you’re using the verb or the noun because it sounds a little like both at the same time.
Although these kinds of things are important to study and know, you should also find a native speaker to practice these with. Have him or her model the two words in a natural sentence for you so you can hear the real difference.