Does anyone know about timing belts?

we have a 93 infiniti j30 and we had a mechanic fix the head gasket, the intake (something) and the exhaust gasket ( or something like that) and he fixed the timing belt and the part that actually turns the belt... anyway we tried to start it but it didnt start! So now we think its the timing thats off because he didnt set the timing right! does anyone know what time its supposed to be set on or any suggestions on what we should do!