Ehh... maybe I should have looked for it on the cPanel first, but I had no idea it was there. >.<
I will try doing that, but I don't see how it would work if just typing in HTML, PHP, and even clicking the buttons didn't help me out. Can I use PHP in the error pages?
EDIT: Just found something out: there is a new 404.shtml page in my File Manager. Do I need to do anything related to this?
EDIT again: I attempted to edit the 404.shtml file with my regular site layout; no results as far as I can tell. Do I need to have a certain ad-supported deal with x10 in order for this to work or something?
EDIT: I think I fixed my problem. I found another tutorial on the net, and I found I have to edit the .htaccess file and enter "ErrorDocument 404 /404.shtml".