Default Install All Apps on SD card On Micromax Unite 2

Hello All,

Recently i bought Micromax Unite 2, its a good phone but what problem i am facing is that it comes with internal storage of 4 GB and has external storage and i am using 8GB SD Card.

Under storage it shows free Internal storage of 0.90 GB(free 100 MB), External Storage of 7.47 GB (left 6GB free) and Internal SD card of 1.67 GB (left 1.67 GB free). By default it install apps on Phone/Internal storage and its getting filled and i am left with only 100 MB and it get hanged.
  1. First i want to know what is the difference between Internal SD Card and phone storage??
  2. Can I install all apps on Internal Storage(which is 1.67 GB free) and External Storage?