endowment fund is like a trust fund. The money will be put aside and not use. Only income generated from the fund is used for expenses etc. For example, NKF have say 260m reserves, they put 200m into this endowment fund, it will in turn place into a mix of say Fixed deposits, bonds and equities. Income from the fund, such as interest from FD, payments from bonds and dividends from equities are then use for its day-to day operations.
Most trust funds and Foundation works this way. Usually it will be governed by a Board of Trustees and advised by professional bankers/lawyers/accountants etc on usagae of funds.