Report is a program which can provide user the specific information data that he/she is looking. Let's say, for a city everyday how much business is going on is need to check by the city Manager. So at the end of the day he will simply run a report with today's date and he can see the details.
In ABAP we can create a report by SE38 transaction.
Generally a report will not update or change any data in the database. It should have a selection screen where user can choose the criteria based on what he want the data to display. The output will be generally in a tabular format, like excel sheet display with columns & rows.
Any program we have to create starting with Z.
To create a report, go to SE38 transaction and provide any name starting with Z. Then press create, a pop up window will ope. We need to fill the details like below screen.
Then click on save button and start writing your code inside the editor.
After writing the code click on the activate button. You are done with the simplest ABAP code.