All transactions on the Lamden Network are smart contract transactions.
When you create a transaction you are specifying:
nameof the smart contract.
method/functionof the smart contract you want to execute.
argumentsto provide to the smart contract.
Transactions on the Lamden Network are paid for in "Stamps". Stamps are converted to TAU in the system and deducted from your wallet balance. If you do not have a sufficent TAU balance then your Tx will either fail to be accepted by the network or fail during execution.