Alright, I got a cube, a long and a straight one. I would like to make few round holes in it. How can I achieve it the best way? Boolean difference I thought first. I tried it but i could only make one hole using a tube. Second hole already said that the meshes should be closed. Thank you for your help.
delete one side of the cube
add a circle [or several] aligned with this one side
select the circles and the part where you deleted the face from, and hit shift+f to fill the region
this doesn’t work with subsurfacing [you’d need to work with it a lot, it’d be easier to extrude the face to make a hole that way]
The hole should go all the way through the cube so you could watch through it.
When you have got a plane that has a hole, you can extrude it (with e key) to form a cube. (note: all verts of that plane need to be selected before extruding)
It does fill the circles.
You need to select all the verts before hitting shift-f. If you selected only the circles, it would fill only the circles as in the picture.