He is doing leveraged bets that the QQQ stock fund will go up a certain amount. When it goes up to that certain amount, he makes another bet it will go up again.
At the same time he is using a call spread so the upside is limited to the difference between the contract he bought and sold. Also at the same time, losses are limited.
Suppose $TWTR is $49 a share, you buy a call for $50 and sell a call for $60. Suppose the $50 call is $3 that means you paid $3. Then you sell the $60 for suppose $1. So now you are out $2. That's your max loss.
Now tomorrow $TWTR goes to $35. Everything expires and you lose $2.
Suppose it goes to $300. Then your profits are ($60-50)-$2=$8 Profits
Suppose it went to $55. Suppose this is after expiry, then your contract is worth $5 but you paid $3 so you made $2 profit, but you also sold 1 contract, so now you have $3 profits.
So in essence, the spread limits your upside, further limits your downside while you are bullish.
