Enterprise Manager

Hello,

I will have Oracle courses only in October.
But I had to develop a backup routine for an Oracle system we have here. (11.2.0).
The database server is based on Windows Server 2008 64 bits.
I have access to Enterprise Manager and sql plus, but I've chosen Enterprise Manager.
I've been reading the 2-day manual, but I didn't understand some things...

The first thing I did was to activate the archivelog mode.
When I activated it, it was pointing to D:Oracle\product\11.2.0\dbhome_1\RDBMS.
But after the restart, the archivelog is activated, but it's pointing to USE_DB_RECOVERY_FILE_DEST.
How do I do in order to discover this directory ?

I also schedulled a job to perform backups by using Oracle Suggestion in Enterprise Manager.
The first execution took a long time to finish. But according to what I've read, this seems to be normal for the first backup full.
And it has generated some big DBF files in my backup folder.
The second backup full generated only a .bkp file
I just want someone to confirm that this is ok.

Now I also have some .ARC files since the day I activated the archivelog mode.
I only have the last .BKP file, but the .ARC files are accumulating. I already have 3 days.
How do I configure this on Enterprise Manager ? How many files Am I supposed to keep ?

Eduardo