Photo-sharing app popular with 50% of stars (5)

'photo-sharing app' is the definition.
I don't know anything about this answer so I cannot judge whether this works.

'popular with 50% of stars' is the wordplay.
'popular' becomes 'ita' (I can't explain this - if you can you should believe this answer much more).
'with' is an insertion indicator.
'50% of' suggests halving the letters.
'stars' becomes 'suns' (sun is a type of star).
'suns' with half the letters taken is 'ns'.
'ita' placed around 'ns' is 'INSTA'.

Can you help me to learn more?