What does "spell out" mean?
Make plain, clarify, as in We asked her to spell out her objectives. [c. 1940]
Read slowly and laboriously, as in He was only six but he managed to spell out the instructions. [Early 1800s]
Puzzle out, manage to understand with some effort, as in It took years before anyone could spell out the inscriptions on the Rosetta Stone. [Late 1600s] All three usages transfer spell in the sense of “proceed letter by letter.”
Learn more about spell out