To Crispr edit you need two things. One is an enzyme known as Cas. Cas’ job is to cut DNA. The other is a piece of DNA you manufacture. In the simplest terms, one piece of the dna binds Cas and the other binds the DNA of the target. When you combine both parts you create a little homing missile that binds the target so that Cas can make a cut. Now there’s a whole bunch of neat tricks you can do but the simplest are either to make a mutation or add DNA.

Just by having Cas at the target, the DNA will keep getting cut and the cell will repair it. Until it doesn’t because it makes an error. Then because your manufactured DNA doesn’t match the target perfectly it dissociates and Cas stops cutting. Now you have a missense, silent, frameshift, deletion, or nonsense mutation.

Alternatively, while Cas cuts you can also add more DNA that matches the DNA around the target with the hope that when the cell repairs the DNA and that this new DNA sneaks in. Now you have an insertion.

Again lots of little tricks you can do. For example let’s say you want to mutate a protein important in heart muscle. You can literally use CRISPR to insert an artificial gene that is only expressed in the heart by sticking close to a gene sequence that is only expressed in heart. Then you can actually CRISPR in the Cas protein but in a way that it’s only turned on when exposed to a chemical like the chemo drug tamoxifen. So you can grow normal mice and then at whatever point you like expose them to tamoxifen which turns on Cas. This Cas will then only have an effect on your original gene target only in the heart because the artificial DNA sequence you added is only expressed there. Really the possibilities are endless.