Q.1) What are SAP reports?
Ans: SAP Reports are event-driven programs using ABAP/4 programming langugage. These reports are used to fetch business-specific data from SAP standard databases under specified selection criteria, fetched data is processed to display result on output screen. User develop SAP report object on ABAP editor using the standard SAP transaction SE38.
Q.2)What are [...]

If i_final is the final internal table containing  retrieved business data, and w_final is the work area of your final internal table, then you can display the result (classical report view) by writing code in following manner.
*&———————————————————————*
*&      Form  TOP_OF_PAGE
*&———————————————————————*
*       For data display
*———————————————————————-*
form TOP_OF_PAGE .
IF NOT i_final[] IS INITIAL.
ULINE.
WRITE:/1 sy-vline,
2 ‘PO Number’,
12 sy-vline,
13 ‘PO Line Item’,
25 sy-vline,
26 [...]

There is no mandatory event in a report program. Events are actually used to organize the statements and control the flow of the program. If the program contains no explicitly defined event blocks, all the statements in the program form the entire event block START-OF-SELECTION. ABAP runtime environment automatically introduces a START-OF-SELECTION at the first [...]