Install All Apps on SD card On Micromax Unite 2
For 1) you can think of them like different partitions of a disk. Internal SDCard usually is found at /sdcard (though not always directly mounted there), while internal storage (as referred to) usually goes to /data. More details can be found in our tag-wikis on storage, internal-storage, and file-system.

For 2), most likely not all apps. And if you can do so at all also depends on the Android version used.