Hi,
I am not good in electronics, I bought a second extruder and a fan for the new one, But now I don't know where in ramps I can connect the fan wires? Please help me.
Thanks

What do you want to do with the fan? Is it just to cool the hot end or do you want it to b g-code controlled. If the latter, then you do not need 1 per hot end. 1 is enough. If the former, then you just need to wire it to your power supply since this type of fan should be always on

Direct wire, or use an unused pin with a fan controller. There are several on thingiverse that are easy to build yourself, or get a premade one.