Syllabary Sa is a simple list of about 200 cuneiform signs with their value and their names (e.g., SpTU 4, 196 [/cams/gkab/P274497]). The ordering of the signs in Syllabary Sa follows three main principles: phonetic permutation (syllables with the vowels u-a-i), homophonic (similar sounds) and semantic (similar meanings).
Vocabulary Sb is a related list of signs with their values, names, and Akkadian translations . However, the ordering of the signs is more graphical (similar appearance) than in Syllabary Sa. Three Uruk manuscripts contain both Syllabary Sa and Vocabulary Sb. Other examples of tablets bearing both texts are known in Babylonia; they were obviously taught together.
After learning cuneiform signs, the young apprentice would learn proper nouns, gods' names and thematic lists of vocabulary. All three kinds of exercise are attested in Late Babylonian Uruk.
Marie-Françoise Besnier
Marie-Françoise Besnier, 'Syllabaries and Vocabularies', The Geography of Knowledge, The GKAB Project, 2019 [http://oracc.museum.upenn.edu/cams/gkab/Scribalapprenticeship/Lexicallists/PhaseI/Syllabaries/]