Im new with this and I dont know how to make some parts of the shirt transparent (to show the avatar's skin color). Can someone tell me how?

You can't do that.

Oh you're making a shirt, my bad. Which editing software are you using?

Inkscape

Woops my bad, I mean Photopea, its like Photoshop but online

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click the blender options by right clicking the layer and it should show transparency options

nope, i cant see that option, can you send me a tutorial about that?

nevermind, i figured out. is this one btw (its my first shirt ok?) polytoria.com/store/28710

Item

ミラクルミュージカル (Miracle Musical) - Hawaii: Part II shirt

Hawaii: Part II by ミラクルミュージカル on Spotify, Youtube/Youtube Mu

polytoria.com/store/28710