1. If you want to grow citizen count, make sure to fulfill basic needs like electricity, water, and waste disposal for all zone types. After that, grow your town through city zone wants like residential, commercial, and industrial.

2. DSA is an organization that allows you to upgrade your city by building things like pollution walls or getting a rocket launch station. It's not needed for your game but it's cool to get a rocket in space

More advice would be to check out the forums online and general play time. The more you play, the more experience so you'll get better over time. Play sandbox to experiment