Let there be lights in the sky
This is a command. By commanding that lights should exist, God made them exist. (See: rc://en/ta/man/translate/figs-imperative)
lights in the sky
"things that shine in the sky" or "things that give light in the sky." This refers to the sun, moon, and stars.
in the sky
"in the expanse of the sky" or "in the large space of the sky"
to divide the day from the night
"to separate the day from the night." This means "to help us tell the difference between day and night." The sun means it is daytime, and the moon and stars mean it is nighttime.
let them be as signs
This is a command. By commanding that they should serve as signs, God made them serve as signs. AT: "Let them serve as signs" or "let them show" (See: rc://en/ta/man/translate/figs-imperative)
Here this means something that reveals or points to something.
"Seasons" refers to times that are set aside for festivals and other things that people do.
for seasons, for days and years
The sun, moon, and stars show the passing of time. This enables us to know when it is time for events that happen each week, month, or year.
Let them be lights in the sky to give light upon the earth
This is a command. By commanding that they should light the earth, God made them light the earth. (See: rc://en/ta/man/translate/figs-imperative)
to give light upon the earth
"to shine light on the earth" or "to brighten the earth." The earth does not self-shine but it is lit and so reflects light.
It was so
"It happened like that" or "That is what happened." What God commanded happened just as he said it should. This phrase appears throughout the chapter and has the same meaning. See how you translated this in Genesis 1:7.