Welcome to the forums!
It's not you, all of the Android makers do a lousy job of explaining storage. Probably they are trying to avoid buzzwords, but they don't help.
So here's the deal. Android phones have internal memory that is separated into partitions, just like partitions on a PC hard drive. Typically there can be 6 or 8 or so. Some are used for stuff deep under the hood, like your radio firmware, so you can't look at the user level and get things to add up.
Turning to your X2, you have 8 GB of total internal storage, an optional external sd card, and 512 MB of ram.
The 8 GB are divided into hidden (as I mentioned) and probably 5 main areas:
/system is where the operating system is, including built-in apps
/data is what the name implies
/data/app is where your apps and their data go
/cache is basically the operating system cache
/mnt/sdcard is actually what some call an "internal sd card" even though it's not really an sd card (and it has a standard shortcut called /sdcard)
And then your actual (physical) sd card is usually at someplace like /mnt/sdcard_ext with a /sdcard_ext shortcut, or something similar.
The trouble you are having moving things around comes from Android standardization. While "internal sd cards" are getting popular, they are not standard. And apps want to follow standards. Digital cameras for example store pictures at /sdcard/DCIM (for Digital Camera IMage). And even when you move an app to an sdcard, many will still default to storing data somewhere in /data. Then there are games, many of which store resources to /sdcard as another example.
To get a clearer view of your memory layout, try Quick System Info Pro, free in the Market/Play.
My phone doesn’t have an internal sd card so I can't help further, but I bet other X2 owners can, so I am transferring this to that phone forum for you.
Hope this helps!