How can I create HDR-sky from parts?

Hey there!
Now I’m struggle with creating working sky material from custom textures.
I have six textures of my sky: fornt, back, left, right, top and down. I need to make HDR-skybox from this components, but, actually, I can’t find some tutorials about my problems, I don’t know, what I need to do.

ima throw a google search result in here.

i have not verified the functionailty, but it looks like it works.