Difference between structure and table ?

Structure cannot hold the data where table can hold data.

Customer ,Vendor &Material table names ?

Vendor Master	Tables
Vendor Master (General Section)	LFA1
Vendor Master (Company Code)	LFB1
Vendor master (VAT registration numbers general section)	LFAS
Vendor master (dunning data)	LFB5
Vendor Master (Bank Details)	LFBK
Vendor master record (withholding tax types) X	LFBW
Vendor master record purchasing organization data	LFM1
Vendor Master Record: Purchasing Data	LFM2
Vendor Subrange	WYT1
Vendor Sub Range Description	WYT1T
Partner Functions	WYT3
Customer Master	Tables
General Data in Customer Master	KNA1
Customer Master (Company Code)	KNB1
Assign customer credit card	VCKUN
Customer Master Contact Partner	MASSKNVK
Customer master record sales request form	MASSKNVD
Customer Master Sales Data	KNVV
Customer Master Partner Functions	KNVP
Customer Master Licenses	KNVL
Customer Master Tax Indicator	KNVI
Customer Master Unloading Points	KNVA
Customer master credit management: Control area data	KNKK
Customer master credit management: Central data	KNKA
Customer Master: Legal Control  Sanctioned Party List	KNEX
Customer Master (Bank Details)	KNBK
Customer master (dunning data)	KNB5
Customer master (VAT registration numbers general section)	KNAS
Material Master	Tables
General Material Data	MARA
Material Descriptions	MAKT
Plant Data for Material	MARC
Material Valuation	MBEW
Storage Location Data for Material	MARD
Units of Measure for Material	MARM
Sales Data for Material	MVKE
Forecast Parameters	MPOP
Planning Data	MPGD_MASS
Tax Classification for Material	MLAN
Material Data for Each Warehouse Number	MLGN
Material Data for Each Storage Type	MLGT

Transaction codes in SAP

se-37  Function library.
se -51 Screen  painter screen..
se -41 Menu painter screen.
se -80 Object browser.
se -16 Data browser.
sm -30  General table contents display.

File handling in sap

File son application server are sequential files.Files on presentation server workstation are local files.
sequential files are also called a data set.

what is the difference between macros and subrotines?

1.macro doesn't have any return statemen.but a subroutine
can have 
2.execution time needed for a macro is much lesser than
subroutine
3.memory requirement for a macro is generally heigher
4.subroutine can be classified as stated in Previous
answers..but no such classification is available with macro
although macro can have different types of nested form
5.generally no of instructions in macro are smaller than
subroutine
6.macro is always local to the program that defines it
subroutine may or may not be local.

What is file handling in abap?

ABAP provides three statements for handling files:

• The OPEN DATASET statement opens a file.

• The CLOSE DATASET statement closes a file.

• The DELETE DATASET statement deletes a file.

what is AG stands for in SAP?

AG stands for corporation limited by shares in german language as  Aktiengesellschaft for more information go to below URL.
http://en.wikipedia.org/wiki/Aktiengesellschaft

what is BAPI ?

Business Application Programming interface .

what is the transaction code for smart forms ?

smart forms

what is the transaction code for data browser ?

se16

what is OSS in SAP?

Online Service System.

what are the two main product of SAP AG?

Mainframes system R/2 & SAP R/3

what R indicates in sap R/3?

REAL TIME.

when was SAP AG founded ?

In 1972 by four former employees from Germany.

what is ecc ?

Enterprise Central Component.

what is the transaction code for abap editor ?

se38.

what is erp?

Enterprise Resource Planning.

what is abap?

Advance Business Application Programming.

What is sap?

system application product