Looking for Xray Tutorial

you can't xray the pic you posted to start off. First rule is bras and thick clothing aren't worth trying

Idk what the photoshop equivalent is but in gimp, select the area you want to xray, then select colours > levels, then drag the top bar to the left until it reveals a little more without removing too much detail, then drag the bottom bar the right to lighten it up a little bit if necessary. Then select colours > brightness/contrast, then raise the contrast and lower the brightness until it reveals enough of what you're after. This doesn't always work, sometimes you'll have to use the burn tool over where you're sure the nipples are (just a click or two) to bring them out a little more. Like I said though, bras and thick clothing don't work. For light clothing like a white dress, it might be worth going over the whole selection with the burn tool a little bit first, sometimes it makes the levels step come out a bit better before moving onto contrast

also keep in mind xraying isn't a literal xray, it only enhances information which is already there, so if it's a black dress in a nightclub, xray isn't gonna do shit. Obviously nipples poking through the shirt works, but I've found it works well on stretchy clothing such as sports bras. I guess the material it's made out of allows for millions of tiny holes in it, and anything that lets some level of light in can be xrayed