Eliminating the RNA from your DNA:
This is an optional step for after your DNA extraction. Usually there is no need to eliminate the RNA from your product, but if you quantify (measure the concentration of) your DNA using absorbance measurements (with a spectrophotometer), the RNA can lead you to overestimate your DNA concentration. Some people believe it may hinder PCR reactions. If you run a standard agarose gel to check your DNA, you will see the RNA at the very bottom of your gel.

Some DNA extraction protocols include an optional RNase step at the end. Here is a general one that can be adapted for use after any procedure:

Add 1ul of a 10 µg/mL stock solution of RNase A to your DNA and incubate at 37ºC for 30 min. Recover the DNA by adding 1/10 volume of 3M sodium acetate (pH 6.8) and 2 volumes of isopropanol or 95% ethanol to the DNA containing solution. Incubate on ice for 10 min Centrifuge at maximum speed for 5 min at room temperature, to pellet the DNA. Discard (carefully) the alcohol. Wash with 70% ethanol and dry DNA. Dissolve in TE or dH2O, as you did in the DNA extraction.

Alternatively, if you know you want to RNase treat the DNA before you extract, and you are using a protocol with a chloroform step, you can add the RNase A to the aqueous layer after it is taken off of the chloroform layer, let sit at room temperature for 1/2 to 1 hour. Then precipitate the DNA as you would normally.