T-code is a SAP command through which we can get into a particular application.The below T-codes are very useful for ABAP Developers who are working with Core ABAP concepts.SE11 Data Dictionary.SE16 Data Browser.SE17 General Table Display.SE24 Global Class maintenance. SE30 ABAP Run-time Analysis.SE32 ABAP Text Elements Maintenance.SE36 ABAP Logical Data Bases.SE37 Function Module Explorer.SE38 ABAP Editor and Program Development.SE41 Menu Painter.SE51 Screen Painter.SE63 Text Translation.SE71 SAPSCRIPT Layout Set.SE72 SAPSCRIPT Styles.SE80 ABAP Development Workbench .SE81 SAP Application Hierarchy.SE84 SAP Dictionary Information System.SE93 Maintain Transaction Codes.SA38 Execute A Program.****************************************** The tables provided by SAP are called standard table. Some of the standard tables provided by SAP are listed here:- These tables are used for storing master and transaction data.Master data is the one which does not change frequently. Transaction data change frequently.KNA1 = Customer Master dataLFA1 = Vender Master dataMARA = Material Master dataVBAK = Sales document header dataVBAP = Sales document item dataEKKO = Purchase document header dataEKPO = Purchase document item dataVBRK = Billing document header dataVBRP = Billing document item dataMAKT = Material descriptionMARD = Material storage dataMARC = Material plant data----------------------------------------------Table classification based on client concept.Client dependent tablesClient independent tablesThe Tables which contain client fields are client dependent table. One such example of field is MANDT. This field has a identification for client. In client dependent table the client field will be the first field in table.The table which does not contain client field, records in these tables is not specific to client.In ABAP every table must have one primary key and maximum of 16 primary keys. The primary key field should be at beginning of the table.