Hi Sravan,
this TC are transactions of the position management within the SAP TRM (Transaction Manager).
TPM1/TPM2: you can execute the revaluation of positions (e.g. generating unrealized gains and losses of positions) - inclusive reversal
TPM12/TPM13: display the positions and the flows of your treasury positions
TPM18: execution of derived business transactions of your positions
TPM20: display the postings of your treasury flows
TPM28/TPM29: with this transactions you are able to repost existing positions from one accounting assignment reference to another - including reveral
I hope this will give you a little bit more understanding.
Cheers
Robert