The backface of quads are rendered

[Mihai_Ionut_Floares]

https://streamable.com/mielrx
Why is rendered the inside of the cube?

[KaiHH]

Have you enabled backface culling, then?
https://learnopengl.com/Advanced-OpenGL/Face-culling

[Mihai_Ionut_Floares]

No. I enabled only the depth test...
And that line that I don't really know what it does: glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

[KaiHH]

No. I enabled only the depth test...

Well... you need to enable backface culling then. Please read the referenced article.
And about what glClear() does: You can always just search/google the function names, you know, and you will get the documentation for that
-> https://www.khronos.org/registry/OpenGL-Refpages/gl2.1/xhtml/glClear.xml