Finance is the application of the principles of financial economics to an inter-related set of monetary problems. In the case of a company, this generally involves balancing risk and profitability and is typically called managerial finance or corporate finance. Investment theory is concerned with the identification of an optimal portfolio of assets, given a set of objectives and constraints, as well as with the valuation of assets. Finance can also be used by individuals (called personal finance), and by governments (called public finance).
For material covering three areas in finance - corporate finance, valuation and investment management, see Prof. Aswath Damodaran: http://pages.stern.nyu.edu/~adamodar/
For articles on current corporate finance and investment issues, visit Oaktree Research, a financial education portal: http://www.oaktree-research.com