Must a beginner memorize all sixty-four hexagrams first?
No. Start with yin and yang lines, the eight trigrams, upper and lower structures, line order, and the relationship between the primary figure, moving lines, and changed figure. Memorizing names without structure rarely helps with a real question.
Study one figure at a time: draw it, describe its interaction in your own words, and compare reliable commentaries. Repeated comparison is more effective than trying to memorize everything at once.