Sometimes, people don't realize this until it is too late, but "nonprofit" does not mean "needs no money." It simply means that profit is not the fundamental purpose of the organization. Not having profit as a fundamental purpose usually means you are providing a product or service that is not cost-effective or the target audience cannot afford it on its own. How do you make up the shortfall?
Here are the major ways to fund your nonprofit:
Self-Funding. You or the board simply pays the expenses out of their pockets. For accounting's sake, it would be preferable that the board donate money to the nonprofit which is deposited into the nonprofit's account, and then the nonprofit pays its expenses.
Fiscal Sponsorship. If there is a 501(c)(3) with a similar mission that is willing to fund your programs (not the organization), then you could request that that organization become your fiscal sponsor. Fiscal Sponsorship is a contractual obligation between both organizations. A fiscal sponsor provides funding for a program and the funded entity can be an individual, a for-profit, a nonprofit or a tax exempt nonprofit (a 501(c)(3) organization.) It is worth noting that much like most grants, this is NOT money that can be used for anything. The proceeds from a fiscal sponsorship agreement can only be used to fund the agreed program. A program is a well-defined and budgeted activity with timelines and measurements. The fiscal sponsor will manage the money, your organization manages the program.
Donations. Your organization can fund-raise from the public. This can be the time that you discover your mission is "important to you" but many people do not consider it "important." Starting a GoFundMe or similar drive takes very little work, but if you don't have a wide set of supporters, strangers are probably not going to send you money.
Grants. Grants, like fiscal sponsorship, fund programs, not organizations. Most funders will expect a line-item budget for the program as well as one for the entire organization. They will want to see your corporate paperwork and your 501(c)(3) letter of determination. They will want to know how you are defining and measuring success and what your organization has done in the past. Many will require that you have been in business for a number of years before you can apply.
Service Fees. Your organization can charge fees for the services it provides. The fees may not cover all of the program's expenses, but it may cover some - think of an animal rescue's adoption fees. While $300 may seem a lot to adopt a puppy, the rescue may have spent thousands on rehabilitation, depending on the condition of the animal when it entered their program. Fees will have to be reasonable for your area, your services and your target market. If your service is directed at the low-income population, charging fees may not make sense.
Unrelated Income. Your organization can have services or products that are not related to your mission. (A pet rescue could run a thrift store.) This income is subject to tax and must be reported on your Form 990 each year. My usual concern about unrelated income is that often it takes over the focus of the organization, and suddenly, you are running a thrift store that rescues pets on the side. Your mission must always be your primary focus. The IRS will also look at how much income you are generating with your unrelated programs.
I will never say "never", but you are probably not going to get grants for the first two to three years of your organization's existence. Your organization cannot be sitting around waiting, either, since funders will want documented results before they consider funding your programs.
I will never say "never", but it is highly unlikely that you are going to start a nonprofit and never have to spend your own money, because somebody else pays for everything (unless you have a wealthy board.) You are going to have to raise money. My favorite way of all the options is service fees, because as the amount of services your organization provides goes up, so does the income from the service fees. If you can set your fees to cover all of your costs, you may not have to raise any other money.