or the "chasis" we will be using the 3D software Fusion 360 https://www.autodesk.com/products/fusion-360/students-teachers-educators (free for students)(You can use another one, as long you don't do any thing to complicated they are pretty similar).
1) Once you download, install and launch de App, You should and on a window that should look like this :If not , go on the second Top left icon and chose "New design"
2)- Onc we are there we can either do a shape and carve it, or the smart way and make a sketch of our project , then we will shape it withthose information we putted down.
To do so, you need to select the "New Sketch" options. For any of them you need to chose a reference plane (the plane were you will be aking your 2D drawing)
From here you can skip to a later part to "press pull" and give some well diserved 3D to your 2D work
2-1)For a design simple as a box made of rectangle we will use the "2 points rectangle" option to make a rectangle. Note thta you can edit either sides parameters freely. Said box will be a 3.8*7.4*3.4cm rectangle with 2 mm wide walls.
So we should have a rectangular base by now , but now you want to have walls ! To do so, re-use the rectangle option and make "wall" patern on the base
(Make thin rectangles on as long as the sides they are suposed to be)(You can use the "Lines" option to make more effisiant and good looking sides)
By this point your project should look more or less like this.
3)Great now we can go on to do 3D stuff !To make this plan go to 3D , use the "Create: Extrude" it will basicaly add depth on the part you want to.
So once you've raised the walls and have a base with a depth of 2mm .
3-1) After this you need to delete 2mm from the top of one of your walls to create the entering side of the top of the box.
Once done we need to add a slide opening in the 2 other walls, to do so , draw a shape (preferably a isoceles triangles)
Once done , extrude those to the other sid of the walls.