An Investment Bank, usually, provides services like,
i. Underwriting services, where the investment bank takes up a task to sell all or some portion of the shares to be issued in an Initial Public Offering (IPO)
ii. M&A advisory services, where it manages the M&A process from start to finish. This is the service that investment banks are most known for.
While a full service Investment Bank offers variety of services (including the above mentioned services) like,
i. Sales & trading, where the investment bank can act as an agent to clients or invest its own capital to trade in stocks and bonds. Since, most of investment banks are involved in dealing for both internal and external clients, they must maintain a Chinese wall (An information barrier between these two divisions to prevent either side to profit in an unfair manner)
ii. Equity research, where the investment bank publishes research reports on various stocks to help investor to make a trade decision on a stock.
iii. Asset management, where the investment bank manages investments of the investors.