After learning all the pronunciation rules of English, like getting your tongue between your teeth for a ‘th’ sound and getting your tongue far back in your mouth for a strong ‘r’ then there is still a roadblock in speaking English naturally and that is stress.
I’m not talking about the stress you feel when speaking English (although that’s an issue too) I’m talking about the way that native speakers add stress to certain words in sentences. The three ways of adding stress are with volume, duration or pause.
Volume: “I love you”
Duration: “I love you”
Pause: “I love you”
In all of these sentences ‘love’ was made more important by adding stress to it. English speakers usually use volume when adding stress, so don’t worry too much about the other two.
Stress can really change the meaning of a sentence.
“I love you” = I am the one that loves you, not others.
“I love you” = I love you, not hate you or other emotions
“I love you” = You are the one that I love, not others.
Since English doesn’t mark the parts of speech (like subject, verb and object) with particles like some Asian languages the stress becomes useful sometimes for figuring out meaning. This is also the reason that English native speakers sound a little funny when speaking languages like Korean or Japanese since they usually add stress into languages that don’t need it.