Conventions of the digipak form

What is a Digipak and how it is similar/different to an album cover?

A digipakia type of packaging for CDs or DVDs which is typically made from cardboard with a hard plastic interior to hold the CD or DVD.
A digipak is a version of an album and offers extra tracks or bonus features.

what does a digipak net look like and how many faces are usual?

A digipak is net of folded cardboard or paper which usually consists of 4-8 panels.

what do we usually find on various faces of the digipak?

on the front of the digipak you would normally see a close up of the artist so you can recognise their face. you would also see the na,e of the album on the from cover and the artists names would also be on the from cover.

on the back of the digipak you would normally find a track list of the song on order of the cd. you would also find in small print at the bottom the record label and then to one side the barcode and maybe the price. 

in the inside of the digipak you would find a CD tray and sometimes a lyrics book would be on the indeed from cover.