Once you have progress and traction for your venture, you're ready to start looking at early-stage funding sources. Thee most common sources of early-stage funding depend on the type of business you are building. For small businesses, you'll want to look at bank loans from local banks or micro-lenders. For startups, accelerator programs and angel investors are the best early-stage source. For nonprofits, now is when you start writing your first grants and soliciting the public for donations, if you have tax-exempt status.
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.
This question has a pretty clear-cut answer - you should open a bank account for your venture as soon as possible. You can use your EIN number (which you can get online for any type of business, even if you are not incorporated) to open up a business banking account at any commercial bank. It is a good idea to do this sooner rather than later, because it can be difficult to look back and figure out what was, and was not, a business expense if everything is going through your personal account. This can make it hard to know how much you are earning (or spending) per month, how much personal capital you or others have contributed, and how the venture's finances look in general. If you choose a local credit union, you can likely open up a business banking account with No or Low monthly fees.
Venture Capital is a very specific type of equity capital that is utilized by high-growth startups. The vast majority of businesses (over 95%!) will never take VC, because the structure of venture capital essentially mandates that it can only be used by companies that have the potential to access $500m+ markets. The reason for this is that investing in high-growth, early-stage startups is super risky - there are a million reasons why any given company might fail. Because of this, the venture capital firm is going to end up losing money on most of their investments. In order to make a profit, the VCs are relying on 1-2 of their portfolio companies hitting it big - think an Uber or Facebook. The massive returns from these companies make up for all of the money that was lost on the other 90% of the portfolio. But since it's impossible to know which startups will fail and which will succeed, every single company that gets VC money needs to have the potential to make these massive returns.
The most honest answer to this question is also the most useless: you need funding when you need it! There is no good answer to this question, because it wholly depends on the founding team's financial circumstances. You might not have personal capital to contribute to your venture, and that's okay! But all forms of external capital come with tradeoffs (even grants, you will spend many hours writing them!) so it's a good idea that you make as much possible progress on your venture that you can before seeking capital.
Debt, Equity, and Grants are the three core categories of funding that you will come across. Each has a large number of sub categories, but this is more or less how they break down: