Why is volume measured in m^3?

Ok im trying to get this SI system of measurement but its so confusing. Why isnt volume a fundamental si unit? How is volume connected to length (meters) how to u go from from meters to liters? and how in does 1 liter= (1dm)^3 = (10cm)^3 = 1000cm^3? try to explain this simply beacuse this is all new to me. Thank you.