Welcome Jeff!
I hope you can get your income up soon--while we strive to live on around 25k/yr here, theres a stark difference between living on 25k and having 25k/yr total at your disposal.
That said, I think you need to get yourself a solid foundation before you consider investing.
You have $20,000.
Do you have any debt? I would pay it off.
I'd then throw about $10000 into a savings account for an emergency fund. Many here are against emergency funds, however, since you do not make much money, you do not have a lot of wiggle room to just "figure it out from your monthly cash flow" vs some others here.
Then I'd take whatever is left and go open an account at Vanguard and begin investing. You should head over to bogleheads.org and read up on their wiki about the "3 fund portfolio" and also visit our friend over at jlcollinsnh.com and read his stock series.
Once you feel you have a handle on it, I'd recommend going over to Vanguard, opening up an account, and set up your asset allocation as you see fit from your previous readings.
The biggest piece of advice I can give you is that as you make more money, keep living how you do. Then pile all of that into investments and soon enough you will be FI!
Best of luck!