Raising investment exchanges a share of the business for money.
How it differs from borrowing
A loan is repaid and the owner keeps the whole business. Investment is not repaid, and the owner permanently owns less of it — see ownership percentage.
Investors also acquire rights: to information, and usually to a say in certain decisions. Those belong in the operating agreement.
Why it rarely fits a service business
Outside investors look for businesses that grow far beyond the effort put in. A trade business generally grows in proportion to its people and vehicles, which is a sound business and not the shape investors are buying.
So for most owner-operated businesses the realistic sources of money are trading profit, borrowing, and the owner's own funds.
Bootstrapping
Funding growth from retained earnings — slower, and it keeps the whole business and every decision with the owner.
For a business that can grow at the rate its profit allows, this is usually the better arrangement, and it is what most successful trade businesses actually do.
Grants
Money that is neither repaid nor exchanged for ownership, usually tied to a specific activity — equipment, training, hiring, energy efficiency — and to a defined region or sector.
Worth checking for, because the cost is only the application. They rarely fund general operations.
Crowdfunding
Better suited to a product with an audience than to a local service business.
If it is being considered
The valuation, the rights attached, and what happens if the business needs more money later all matter more than the amount raised — see business valuation. This is a decision to take with an attorney and an accountant.