The SBA is a standalone US federal government agency created in 1953 to help American small businesses through financing, training and advocacy. Most of its financing assistance comes in the form of loan guarantees; banks lend money to the business and the SBA guarantees payment on most (but not all) of the loan if the small business defaults on the loan. Not surprisingly there are guidelines and paperwork to qualify.
In addition to general business loans called 7(a), there are also microloans, disaster loans, real estate/equipment loans, and export loans. There are both videos and blog posts that explain all of this here on the SBA web site.