How to use colorimeter

I need help clarifying my idea on how to use it to find the concentration of a solution.
Are these the steps?:
Zero the colorimter using distilled water
Set the filter to the complimentary colour of the solution being tested
Make solutions of known concentrations (and make them the same colour as the solution your looking for the concentration?)
Measure the absorbance of each solution and plot them on a calibration graph.
Measure the absorbancy of the solution and read off from the graph to get the concentration.

Are these points right and would they score me full marks on questions like these? And should I include the part where I said you have to make the solutions at the same colour as the test solution?

And another question. Im a bit confused about the idea of DNA replicating itself through mRNA. I know that the DAN splits in half, mRNA codes to the DNA codes (A to U, C to G). The mRNA then goes into the cytoplasm in which tRNA bonds to the mRNA and then the ribosome bonds it? Something like that. Can someone clarify my ideas.