Open Source and profit...

I've spent 23 years (on and off) developing an action-planning-tool.
I'm learning C so I can design a prototype so it can be "protected" while I seek venture capital, etc.
My local-closest-to-guru-guy said I need to be aware of open source library use because if I include certain functions/libraries I would not be able to sell the code due to open source "copyright" or is that "left"?
I definitely want to sell the tool; I've worked hard on it, will soon work even harder and feel compensation is due...
Yet..
I'm not greedy...
I do want the tool to be widely used...
Maybe I'd be willing to make the damn thing OS...
As long as some aspect or service connected with it could generate income...
/*Quandry*/
Alex

You should read this.

Thanks, Deckard!!!