All of these refer to those people who have come through the Great Tribulation.
# day and night
These two parts of the day are used together to mean "all the time" or "without stopping" (See: [[rc://en/ta/man/translate/figs-merism]])
# will spread his tent over them
"will put his tent up over them." Protecting them is spoken of as if he were giving them shelter to live under. AT: "will shelter them" or "will protect them" (See: [[rc://en/ta/man/translate/figs-metaphor]])
# For the Lamb ... will be their shepherd
The elder speaks of the Lamb's care for his people as if it were a shepherd's care for his sheep. AT: "For the Lamb ... will be like a shepherd to them" or "For the Lamb ... will care for them as a shepherd cares for his sheep" (See: [[rc://en/ta/man/translate/figs-metaphor]])