How to read the ancient prose in Shuo Wen Jie Zi? There are small characters under the big characters. What is this for?

Is to send words. Take "small" as an example. The word "small" means "small". Small print cuts private signs. Is to pronounce small words, take the initial of the n-th word, and have vowels of both words. Cutting means spelling. The vowel of the personal initials X (different from modern sounds) is AO, which means XAO ... You can try other words in this way, can't you?