Morphemes are the smallest units of meaning in speech. The word “love” is a morpheme. To that morpheme another morphem, “-ing” can be added forming “loving,” a different word. To that, “-ly” can be added forming “lovingly,” still another word.  

They are not the same as syllable.  Syllables break up the speech into rhythmic units.  It is possible for a morpheme to have more than one syllable, as in “rhinoceros,” which is a single morpheme that has four syllables; and it is possible for a syllable to have more than one morpheme, as in “walked” [wɑkt], which has the verb “walk” and the morpheme “-ed” reduced to ‘t.’