Learn about it. I would recommend A Random Walk Down Wall Street [1] and The Boglehead's Guide to Investing [2]. They will give you a good primer, but in essence the best thing you can do it nothing at all. As you get older you'll want to make sure bonds take up a larger percentage of your portfolio, but really you're fine. The old sayings is "time in the market, not timing the market".

[1] - https://www.amazon.com/Random-Walk-down-Wall-Street/dp/03933... [2] - https://www.amazon.com/Bogleheads-Guide-Investing-Taylor-Lar...