How can I fuse a lot of cubes? So, I made a mesh with a lot of cubes ( I've created a cube, and copied it, pasted it to make figures ), And, when I've done it, I tried to smooth it, but it looks wierd because it's made with a lot of cubes, so a lot of faces, I already tried Ctrl + J, but faces remain, Is there anyway to fuse those lot of faces in one?
If I understand right, you need joining cubes without inner vertices.

You can do it in second using Bool Tool addon:

Just select all cubes, (one of them must be active) in BoolTool menu click on "Brush" -> "Union" -> "Apply All" - done

Download Bool Tool