Both are pure bonuses. They pay on top of the coins you earn from offers, surveys and videos, they cost nothing, and they never take anything from your balance. Coins and keys are never sold.
The daily streak
Each day of your 7-day streak pays its own share of what you earned in the last 24 hours, times that day's multiplier, up to a daily cap.
To claim a day, earn the minimum from offers, surveys or videos in the last 24 hours. The Rewards page shows the current minimum, each day's share and multiplier, and the cap.
Each day has its own 24-hour window, counted from your first claim. Miss one and the streak starts again at Day 1. After Day 7 a new week begins.
Free cases and keys
There are four free cases: Bronze, Silver, Gold and Platinum. You open one with a key of the same tier.
Keys come only from leveling up: every new level gives at least one key. The Rewards page shows which keys each level gives.
Opening a case adds the coins of the drop you land on to your balance straight away. Each case page lists every drop, the coins it pays and its chance.
Demo spins a case for free so you can see how it works. It pays nothing.
Provably fair
Every case you open combines your server seed, your username and a nonce that goes up by one with each open into a ticket from 0 to 99,999, and the drop whose ticket range holds that ticket is the one you get. The hash of your server seed is shown before you open, so the seed cannot change afterwards. On the Fairness page of your account you can reveal your server seed to check your past opens; revealing it starts a new seed.