RobH_en_tn/gen/01/20.md

Let the waters be filled with great numbers of living creatures

This is a command. By commanding that living creatures should fill the waters, God made them exist. Some languages may have one word that refers to all kinds of fish and sea animals. Alternate translation: "Let the waters be full of many living things" or "Let many animals that swim live in the oceans" (See: rc://en/ta/man/translate/figs-imperative)

let birds fly

This is a command. By commanding that birds should fly, God made them fly. (See: rc://en/ta/man/translate/figs-imperative)

birds

"animals that fly" or "flying things"

the expanse of the sky

"the open space of the sky" or "the sky"