Using the jAlbum desktop application (Window, macOS, or Linux), you create the album on your computer, then upload the result. You can't then upload additional images directly to that album - it's a finished product. To add images, you have to open the album project in the desktop application, add the images, make the album again, and upload it again.
The jAlbum for iOS app is a different animal entirely. It can be used only to create an album on jalbum.net hosting. You can't use it to create an album anywhere else, or to modify an album that was made with the desktop application.
You can also use the iOS app to view albums created with the desktop application, in a fixed format, independent of the skin that was used to create it. But these days, most skins are fully responsive on mobile devices, so you're better off just launching the browser on your phone and pointing it to the album you want to view.