Every year, Silicon Valley accelerator Y Combinator holds a one day event called Startup School, where rookies come to learn how to start their own company. Last week, attendees were treated to advice from entrepreneurs like Facebook's Mark Zuckerberg, Twitter and Square founder Jack Dorsey, and Evernote's Phil Libin.

You can view the interviews online, but here's a quick rundown of the most poignant advice from each founder.

Mark Zuckerberg on the Power of Passion 

When Paul Graham asked Zuckerberg at what point he knew he created a social tool for the world, Zuckerberg said he really never thought he did until it happened. Looking back, Zuckerberg said he shouldn't have been able to make the world's favorite social media company. "All these other companies [Google and Microsoft] had engineering power, servers, time, and money," he said. The one advantage he had as a 19-year-old computer geek was passion and determination, and not needing to care about a business model in the beginning. "A big reason other companies didn't invest in [creating something like Facebook] was because it wasn't clear there was a business model for it. I think this is true for a lot of the best ideas," Zuckerberg said. "It's not that someone else can't do it--they can and the odds are stacked against you--but that belief that you care so much about what you're doing is the only thing that drives you to do it. This is what drives me to this day."

Jack Dorsey on Building a Team

Jack Dorsey, co-founder and chairman of Twitter and founder and CEO of Square, didn't come out and give quick tips on how to hire your first 10 employees, or how to scale while doubling revenue. Instead, he read from two books that he said have influenced him as an entrepreneur and creator: "The Art Spirit," by Robert Henri and "The Score Takes Care of Itself," by Bill Walsh, the former NFL coach of the 49ers. However, between talking about the importance of creating art for yourself and Walsh's best leadership lessons, he offered advice on how to stay focused as a team.

"One of the hardest transitions [entrepreneurs] have to make is going from individual creation to leading a team. This is something I certainly fumbled with along the way," he said. "As you start building a team, you need to set expectations around how people need to perform and act in the company. This is easy, but without this you are rudderless and will react to the outside pressures."

Phil Libin on Finding Co-Founders and Epic Ideas

CEO of Evernote Phil Libin said the popular organizational tool was the product of strong friendships between co-founders who met in college and built two start-ups before Evernote. "The most important thing to do as a young an age as possible is cultivate a group of really brilliant, high-energy, willing-to-work-for-free, best-friends-for-life," he said. "I'll go as far to say that you shouldn't make friends with people you don't see starting your company with. Why bother?"

For Evernote, Libin said he and his co-founders started with a key mission: to build a company that would last the rest of their lives. After selling two companies and merging with another to create Evernote, they had trouble raising money and staying afloat. They lost a $10 million investment the day Lehman Brothers collapsed in 2008 and were planning on firing everyone the next day. But as luck would have it, Libin received a random email from a fan of Evernote in Europe at 3 a.m., asking if they needed an investment. He gave them $500,000. After that, the investments from around the world started coming in and the company was saved.

Looking back, Libin said the crucial decision he and his team made before they conceived of Evernote was not to sell their next company. "We decided to find something sufficiently epic to do, and that was Evernote," he said. Building something great--something people wanted to be a part of--is what saved them during the 25th-hour, he said. "There's no exit strategy for your life's work."