What is the Index and what does e.g. 5/12 mean?
Nonce (number generated once) is a 81-tryte hash that is output of the Proof of Work hashing once the target value has been reached. Every transaction must have a nonce for it to be accepted by the network. Source: https://learn.iota.org/faq/nonce
A typical transfer in IOTA is a bundle consisting of n transactions, these are recognized by using Index (0,1,2,3,...n)
Index 0 - Output. Recipient of the transaction and Value
Index 1 - Input. first part
Index 2 - Input. Second part
Index n - Input - Output. Balance that is sent back to sender