How indexes are updated

To whom it may concern:

I think I have proven to myself that when a new record is added to a table it is added to the end of the table.  Also,
whena record in a table is updated it is also moved to the bottom of the table.   

Can someone tell me when the indexes on the columns in the table are updated.  Is the insertion of an index record
insertedbefore the new record is added to the bottom of the table?  Or is the new record added to the table  first and
thenthe databse figures out the insertion in the index?  Thanks in advance.  

Bob Powell