if your reading the raw tx details of th transaction..
output is to you, input is from them

another way is to put the txid into blockchain.info and you will see

1addresss  -> 1other address

the address on the left is the sender the one on the right is the receiver(you in this case).

you cannot find the total combined holdings of that user but you can see how much the sender had in that particular address(s) he used to send you funds