I have a amp with output rca jacks wat does this mean?

For passing signal to another amp (daisy chaining) when you don't have another available rca output from the headunit. The only downfall with that is what ever signal is processed into the first amp (EQ, crossover) will be fed to the second amp. So basically you would not be able to add a second amp as a sub or vice versa if you are using the headunit's crossover if that's making any sense to you. If you are only using the amp's crossover then you should be fine as it will normally just pass an unfiltered signal through it's rca output.