How we make a chant--we need scripture, tones, and rhythm tied together by the breath of life. By repeating and adjusting until the chant lives and breathes in us, meditating, obeying.
How we learn a chant--we chant the living words with tones and rhythm by each section 3 times as we can. (recordings are helpful) Change up the section by a video, only text, with only audio-listening or humming, or from memory each change 3 times. As we can chant sections by heart, we stitch the sections together until we have gained the passage. "Riches gotten quickly will dwindle, but those who acquire them gradually become wealthy."
How we keep a chant in memory--(recordings are helpful) Even after 20 years, a passage unbidden will come to mind correctly. But to keep the chants fresh, it is good to review them once in a while.