transaction log in Oracle are knwon as the redo log.
Every instance of an Oracle Database has an associated redo log to protect the database in case of an instance failure.
To protect against a failure involving the redo log itself, Oracle Database lets you create a multiplexed redo log so that two or more copies of the redo log can be maintained on different disks.
You can archive them automatically with the archivelog mode.
The archive and table logging mode is what will dictate whether redo is generated for the table or not: Oracle Database - How to bypass the redo log generation ?
For an index, you can't bypass it: Oracle Database - Why you have still a lot of redo and archive ? The Index side effect.
The redo log buffer is a circular buffer in the SGA (based on the number of CPUs).
select member from v$logfile;