The SBA is the US federal government agency behind the highly popular SBIR / STTR programs. See our SBA article for details.
Following is the description of what SBA does on their official website, sba.gov.
Access to Capital (Business Financing)
SBA provides small businesses with an array of financing for small businesses from the smallest needs in microlending - to substantial debt and equity investment capital (venture capital).
Entrepreneurial Development (Education, Information, Technical Assistance & Training)
SBA provides free individual face-to-face, and internet counseling for small businesses, and low-cost training to nascent entrepreneurs and established small businesses in over 1,800 locations throughout the United States and US territories.
Government Contracting (Federal Procurement)
In keeping with the mandate of Section 15(g) of the Small Business Act, SBA's Office of Government Contracting sets goals with other federal departments and agencies to reach the statutory goal of 23 percent in prime contract dollars to small businesses. This office also provides small businesses with subcontracting procurement opportunities, outreach programs, and training.
Advocacy (Voice for Small Business)
Created in 1978, this Office reviews Congressional legislation and testifies on behalf of small business. It also assesses the impact of the regulatory burden on behalf of small businesses. Additionally, it conducts a vast array of research on American small businesses and the small business environment. The Chief Counsel of this office is appointed by the President of the United States.