Today it seems common that artistic people will get their hands on a “tattooing starter kit” and starts practicing this craft at home. Here are a few points why it may not be a good idea.
This is actually a really bad idea! Your friend could place both of your lives in danger by foolishly trying to learn this at home. Firstly, tattooing on a live skin is nothing like drawing with a pen on a paper. Secondly and far more importantly, home facilities are not possible to be maintained in such a high demand of hygiene as tattoo studios. Also the lack of knowledge in hygiene can lead into critical health issues at its worse, not to mention the lack of technique in tattooing itself which will cause you to live with a horrible scarred tattoo on your body you will end up regretting.
You should tell your friend to get a proper apprenticeship, and when his/hers mentor feels they are ready they can start practicing on you.