Hi I would like to know how transport is happening in sap R3 system

Hi Guru,

Please guide me how this transportation is happening in SAP R3 system. Why do we use three different t-codes (SE01, SE09 & SE10) to transport request from one server to another? also kindly explain what is workbench request and customize request? in what scenario work bench request will be raised and customize request will be raised?

Thanks

Madhu