Listen to the two utterances above and look at the diagrams for each. The diagrams represent the pitch of my voice when I said the utterances. You can see that the place where the pitch fell from high (H) to low (L) is different in the two utterances. In the first the fall takes place in the final syllable name. In the second the fall occurs during the second syllable of remember. I hope you can hear these differences as well as see them.
These two utterances differ in the pace of the tonic (also sometimes called the nucleus). The change in pitch is not always H to L, but the tonic is where the last important pitch in the intonation pattern change takes place.
If you would like to have some practice at hearing where the tonic is, please visit Plato.