1. Just created an account, what do I do? I'm confused
Click the Missions tab, they work somewhat as a tutorial.
2. Why is my happiness so low?
Your work mode affects your happiness. Selecting a less intensive work mode will allow your workers to rest which will yield less income but increase happiness.
Sickness also affects happiness. Train doctors to reduce sickness, which will increase happiness.
3. I'm low on credits, what do I do?
Sell a few units of gold (not all your gold) in the Market . They are worth trillions and you get some gold as reward from some missions.