I have been wondering since a registered to autcraft a few days ago how the autcraft website knows our skins

i think it accesses it by going to namemc.com and putting ur name into it

We have it set to pull your default profile picture to be your avatar as your skin. 

Basically (idk for sure, but this is how I think it goes), avatars are stored in a database as URLs (like https://autcraft.com/forum/topic/3886-how-does-the-autcraft-website-know-our-skins/, but instead of that the link leads to an image) and by default it's an URL from a website which lets people fetch images of player skins (and the avatars we see!) based a player's UUID or username.

Ok, thanks!

Mojang needs someplace to store your skins so that it can access it easily. It stores them on a website that Autcraft has access to, and then uses a Universal Resource Locator, or URL, to find them. This site is also what AutismFather uses when you apply to make sure you don't have any bad history.