Only some guidance, obviously you want to find the details yourself:
Draw a square, add effect "Rounded corners"
Add effect 3D > Extrude & Bevel, preview=ON, no shading, no bevel, the view = Isometric Left. Play with the extrusion depth
Expand the appearance. You get a 2D shape which have the needed curves and anchor points to add more parts. I removed the fill and drawed a green rectangle. It snapped perfectly with snap to points and smart guides ON. Disable other snaps, or you get nothing usable.
You can tweak the effects via the appearance panel as long as they aren't expanded.
You must also subtract parts. That can be done using
- boolean operations in the Pathfinder panel or
- adding clipping masks or opacity masks
- direct path anchor point editing tools and the scissors
You must release the compound path and ungroup the groups before you can edit the expanded shape.
Altough you can often get wanted shapes very fast, 3D effects can be considered as Pandora's Box approach, a shortcut to unnecessary complexity which easily turns to unmanageable => Before trying this explore direct 2D drawing as suggested by others.