I'm new to Blender and I wanted to design this mask in order to print it in 3D but i have a problem. I want the eyes holes to be sharp but the subdivision surface modifier make them round. I tried everything i found on internet to make them sharp ( edge split, ctrl r, crease... ) but none of them works. Could you please help me ? Thank you.
Once you have geometry that can follow an edge loop you can make edges as sharp as you want. CtrlR is the hotkey for creating loops in Edit Mode. Loops require quads. Below I have the example to start...
...and then adding an extra loop to sharpen even more.
I did cheat a bit here as the loops do cross - but it still works and I think acceptable.