There are two primary ways to get new dwellers: attracting them via the Radio Studio or through reproduction. Build a Living Quarters and assign a male and female dweller with high Charisma. They will eventually 'get to know each other' and the female dweller will become pregnant. After a few hours, she'll give birth, and the baby will grow into an adult dweller. Alternatively, build a Radio Studio and assign dwellers with high Charisma to broadcast. This will periodically attract new dwellers from the wasteland. Be mindful of your resource production when increasing your population; more dwellers mean more consumption.
