Well, grab photoshop if you can its the best sofware for this specially for warping if not just use gimp.
Download the bleached resources and follow the tutorials (though downloading isnt necessary) you can grab xtra tattoos from here under the template tag or make more yourself.
I suggest starting with tattoo edits and then moving on to skin edits once you get the hang of warping and such, it'll feel like muscle memory.
Unless you're making money off of this, i implore you to take this as a hobby. Edits will take time and stress can make you think it doesnt look good enough and make you delete minutes if not hours of progress. Ask for help in the forums whenever you need and take criticism, it will help you know your weak spots in editing.