Just try to remember the sap terminology of representing the business or buisness objects... such as
all vendor tables start with L such as lfa1, etc..
all customer tables start with K ... Kna1, konv...
all sales tables start with V... vbak vbap
all master data tables start with T... T001, t001w
all bank tables start with B.. Bknf, bkpf....
all purchasing tables start with E.. ekko, ekpo etc..
all material tables start with M... mara, makt, marc...
in sales, delivery, billing, purchasing...
if the tables name contains K init it is Header data
such as vbak, likp, vbrk, ekko...
if the tables name contains P init it is Item data
such as vbap, lips, vbrp, ekpo ....
Coming to FI tables... there are only 6 important tables in whole Finance module which are mostly used by abapers.
They can be remember by:
if the table name contains I, that is open item
if the table name contains A, that is closed item
if the table name ends with S, that is GL account
exp BSIS- GL master open items
BSAS- GL master closed items
if the table name ends with D, that is customer
if the table name ends with K, that is vendor
Finally, table TSTC contains the list of all transaction codes.