How to make custom skins in gimp

Hi i wanted to make skins for my vehicles but since i dont have photoshop i had to use gimp and paint.net but for some reason everytime i open the file it gives me the checkerboard transparent pattern while tutorials on youtube have no problem. Anyone have a fix for this or a different way to open the files?

i am starting this rn aswell, you need to decompose the layer into rgba. here is the link from the guys that i am watching rn. still if i paint on my tank body it is dont displayed in game… thats another problem lol.