The LSMW (Legacy System Migration Workbench) is a tool used to transfer data from legacy systems to SAP periodically or once. It supports converting data formats and can transfer data using Batch Input, BAPI, IDoc or Direct Input. There are 14 standard steps to transfer data using Batch Input. The LSMW provides a wizard interface to guide the user through each step sequentially to complete the data conversion and transfer. Key steps include mapping source fields to target fields, specifying file formats, reading and converting data, and running the batch input session.