Melinda Gates explains the best way for 20-somethings who are just starting their careers to make an impact in philanthropy

Melinda and Bill Gates have devoted much of their adult lives to philanthropy.

Over the course of their lifetimes, they've pledged to give away 95% of their wealth, and they've already donated billions of dollars to all sorts of causes all over the world.

When the Gates' pledged to give away the majority of their wealth, they were in their late 40's and 50's.

Recently, Mark Zuckerberg and Priscilla Chan pledged something similarly generous - to give up 99% of their Facebook shares over the course of their lifetimes. They're in their early 30's.

Thanks in part to their very public shows of generosity from the Gates' and Zuckerbergs, more and more people are looking to get involved in philanthropy at a younger and younger age.

But most millennials don't create multi-billion-dollar companies, and they don't have significant salaries or deep bank accounts that allow them to give away much money.

We spoke to Melinda Gates at the World Economic Forum in Davos, Switzerland and asked her the single most important thing millennials can do to start making big philanthropic impacts early in their careers.

Gates encouraged millennials to look for ways to give back in their own back yards, and to give away their time instead of money if they can't afford it. She encouraged them to look within their communities for giving opportunities, whether it's spending a morning in a soup kitchen or helping at a local shelter. Gates says even just one hour per month is enough time to make a significant impact in the community.

Gates also said it's important for young people to choose who they mary wisely. She noted that Priscilla Chan is a significant reason why the Zuckerbergs have been able to be so generous. "Priscilla brings a different perspective than Mark does, and so they're able to accomplish more together," Gates said. "I'm excited to see what Priscilla and Mark do as a team."