There are many organizations and individuals which offer money in exchange for something from your company; your decision to borrow money should be based whether what they are offering fits your business model. Typically funding can be divided into debt financing or equity financing. Debt financing obligates your future income to repayment of a loan over time with interest. Equity financing means that you will give up a portion of the ownership company and potentially some control in exchange for money (e.g.: a partner, angel investor, venture capitalist firm…). Both sources of money have pros and cons and it will be up to you to negotiate the best deal you can in order to support your company.
A business loan is a good option for many companies. Formal sources of loans are typically financial institutions (banks, finance companies, credit unions…) and microlenders; semiformal and informal sources include peer to peer networks, your business associates, friends and/or family. For established companies with good financials, banks are likely to offer the best terms though their interest in you will be based on their confidence that you’ll be able to pay them back (good business plan, evidence of net profit, available collateral...)
If your applications for a bank loans aren’t accepted (don’t be put off by one rejection), you can look at microlenders or less formal programs or you can explore Small Business Administration (SBA) loan guarantees. The SBA doesn’t make direct loans but works to encourage banks to make loans by guaranteeing that the bank will receive most of its funds even if the borrower defaults. If your bank doesn’t suggest that an SBA loan guarantee would be appropriate, you may want to contact a bank on the SBA participating lender list. The level of paperwork varies based on the specific SBA program into which you are enrolled by your lender. More information about the SBA’s loan programs can be found at the SBA.