First, congratulations on breaking free of the terrible legacy you youself inherited. Well done.
In terms of your own legacy, the biggest luxury you have is the time to figure that out yourself. What specific issues concern you most? Find local organizations that do things you care about. Volunteer there, see how they work, see where the needs are, see what are effective and ineffective ways to address those needs. That may encourage you to donate to certain things they do -- or it may encourage you to find a different organization if the first one isn't cutting it for some reason.
There also doesn't have to be a single right answer. Maybe you donate some money to a scholarship fund, donate some time and money to Habitat for Humanity, and donate your time being a Big Brother/Big Sister to a kid to provide one-on-one support. Or you could go back to school to get a degree in some sort of counseling area so you can spend your time helping other kids like you were break the cycle. Or if your skill set is marketing, you could help your chosen charity develop fundraising campaigns and knock on doors to bring in money from other people like you.
Etc. Etc. Etc. There are a million ways to help. The trick is finding the options that suit both your interests and your skill set. When you find the "thing" (or things), you will naturally gravitate to spending more time and money on it. The important thing is to just start looking, because the sooner you start looking, the sooner you will find it.