To make electricity, you need to move charged particles.  Most of the electricity we humans use comes from moving electrons in wires with magnets and coils.

When the magnet moves in the coil, current is produced in the coil.  If you want a lot of current, you need to move a very strong magnet in a very big coil...

There are several ways to make magnets move in a coil.  You can boil water and use the high pressure steam to spin a turbine (which is a big fan), you can put your turbine out in the air and let the wind do the work...

or you can just use falling water...

http://www.cornwallis.kent.sch.uk/intranet/subjects/science/ks4energy/hydro.htm