how do i put my custom level in MBU?

I did a custom level but i dont know how to putt it in MBU (Haxe Windows Version, NOT web), Should i use PQ or what??

Upload it on Marbleland, then it will show up on the custom levels menu, as long as you have marked it as MBU.

And how do i make an MIS file for that level, Do i extract my MBU game??

Build a level in PQ, but use regular MBP powerups/shapes/pads. But change the game info to MBU. You don't need to add anything extra that PQ has for MBU.
See how these levels did it:
marbleland.vaniverse.io/level/32764
marbleland.vaniverse.io/level/36017

You can just copy their mis file and edit it for your level.