Add-ons are located in scr folder. Basically you upload the content of upload folder to your server. Then go to ACP -> Add-ons and you'll see the button to install it.
Can I just take a moment to say how much I love the fact that we don't have to deal with asking users to find XML files to install? I understand there's an adjustment period for users, but I think it's a much better system overall.
It's an entire system that took a distinctly non-zero amount of time to create, and I don't think anyone would have called for a hanging in the town square if it wasn't added, it was added purely to make the lives of add-on developers and users easier
The icon and link support to create a truly beautiful and informative representation in the add-on list is just a bonus on top of a bonus.