You type in the information through the Presentation Layer via the SAP GUI.
In order to update the database, this data must be manipulated and managed by the processs called "dispatcher".
The dispatcher process picks up the data from the screens and send it to the database.
The dispatcher also assures that all logical unit of work is completed before the data is committed to the database.
It evenly distributes the work it receives to other processes "workers".
It also organizes the activities so that in the end the database is updated and the transaction is complete.