Basically what Marie said. You usually need enzymes to cut and edit DNA. You can cut some out to stop a function of a piece of DNA or even add some in. ZFNs, TALENs are slightly 'older' technologies and CRISPR is the new technology, which is being used for the purposes above. It may be enhanced/improved in the coming years and I wouldn't be surprised if there weren't other DNA editing technologies that appear in the future too.