Some translations set each line of poetry farther to the right than the rest of the text to make it easier to read. The ULB does this with verses 10-12.
The Book of Revelation uses imagery from the Old Testament. For example, John refers to Satan as the serpent. This image comes from the account of the Garden of Eden when Satan tempted Eve. (See: [[rc://en/ta/man/jit/figs-explicit]])
By using the passive voice here, John does not say who saw this great sign in heaven. The translation may be difficult when the subject is unclear, if your language does not have a passive voice. Many English translations use the past tense here and say "A great sign appeared in heaven." (See: [[rc://en/ta/man/jit/figs-activepassive]] and [[rc://en/ta/man/jit/writing-apocalypticwriting]])