That's a VERY vague question. There are a multitude of ways of investing money. Obviously, this site is focused on real estate investing but there are still numerous avenues in this field as well. It depends on what you want to do.
Are you looking for the safest? the fastest? are you looking for a second job? how many hours a week are you going to put into it? should it be passive income?
Safest... go drop it in a savings account. It's federally insured so very safe... but you'll collect about 0.03% interest on it.
Fastest? Go to Vegas and bet on black... you can double your money with the spin of a wheel (course you could lose it too, so do your own risk analysis!)
In seriousness, read around and ask a more focused question. Lots of people to help here but no one that's going to tell you exactly what YOU should do. That's for you to decide.