couldnt make heads or tails of it

Couldnt make heads or tails of it is an idiom used to show that you are not able to understand something. It is usually meant as a general term for being confused about something, but is also typically used in reference to something you absolutely and positively do not understand, meaning not one aspect of the equation seems logical to you. Heads and tails is in reference to each side of a coin, in that you dont understand any side of something.