The Aztecs did not use written words to stand for their sounds of speech. Instead, they used pictures, or glyphs, for their writing system. Some glyphs were drawings of the objects themselves and some were symbols for ideas for example, a shield and a club meant war.
Writing was not meant to serve as a complete record. Priests or trained scribes would usually memorize a story, and they would look at the glyphs to remember the details. Aztec glyphs were carved on objects like stone monuments and tiny jade beads, painted on walls and vases, and painted in a book called a codex.
In their efforts to convert the Aztecs to Christianity, the Spanish destroyed many of the codices. However one Spanish priest, tried to preserve the Aztec history and language. Father Bernadino de Sahagun arrived in Mexico in 1529. He studied Nahuatl, the Aztec language, and learned about Aztec history by interviewing Aztec leaders. He was able to encourage his Aztec assistants to draw glyphs about their history, religion, and culture. This was published as the General History of the Things of New Spain in both Spanish and Nahuatl, and is one of the best sources we have today about the ancient Aztec culture.