Funding idea-stage ventures is one of the trickiest parts of entrepreneurship. Typically, any institutional investor is going to want to see more than just an idea sketched out on a napkin (unless you are a serial entrepreneur who has successfully started lucrative ventures before). Investors will want to see progress, meaning you have taken concrete steps to turn your idea into reality, and traction, proof that other people are as excited about your venture as you are.
The most common source of idea-stage capital is personal savings, although this may not be viable for everyone. Then there is the Friends and Family Round, which is exactly what it sounds like - you get your friends, family, and acquaintances to contribute money if possible. This still isn't going to be accessible to most founders, so the best outside places to look for idea-stage capital are going to be Microgrant/Microloan programs, pitch competitions, and very early-stage incubator and accelerator programs.