There are two to three basic steps in DNA EXTRACTION from cells. The cell must be lysed (broken open) to release the nucleus.
The nucleus must also be opened to release the DNA. At this point the DNA must be protected from enzymes that will degrade it (also called DNAses), and since the DNA is in chromosomes which are quite long and delicate you must be careful not to shear the DNA. Once the DNA is released, it can then be precipitated in alcohol. Many DNA extraction kits have been developed to extract genomic DNA from cells.