Assets invested through an investment fund are managed in accordance with an investment plan determined by the fund's managers. A large number of different investment vehicles may be employed. It's even possible for fund assets to be invested in other investment funds.
Benefits you get by investing through an investment fund rather than in individual investment vehicles include diversification of investments and (ideally) broad investment knowledge and experience on the part of the fund manager.
Compared to passively managed ETFs, actively managed investment funds normally have higher costs. Make sure to inform yourself about possible fees beforehand.