So as of today, I will be the treasurer of my high school's GSA (Gay Straight Alliance) . What should I know before I start?

Get tough skin and get ready for trolls, depending on what kind of school you're at and what geographical region you're in, but just remember you're doing the right thing and you're on the winning side of history. Be ready to serve in a leadership capacity and have an open ear to members who need you and your organization. Lead by example. Come up with ideas for fundraisers, communications, and raising awareness of your group and its cause. Everyone loves witty and sassy flyers and slogans. Maintain a good relationship with the school administrators, since you never know when you might need their help or sympathies. Other than that, have fun, be proud and rock it!