What Is HTML Editor?

Before anyone asks, yes i have enabled HTML in admin panel and profile.

I don't understand when making an HTML page the code just appears? Is this something to do with that red cross on the top left? What is that? And when do i use it?

Please explain to me and i will be v. great full.

Regards,

when making a page, if you see the bbcode editor and a red plus+ with HTML on it, of you click that first, the editor changes to a plain html box with no bbcode and you should now see a green plus+ with HTML on it. there html should show.

Okay Thank you so much!