Oracle SecureFile - DBFS If I create a table that has a SecureFile column, does it mean that all the LOBs put into the column are automatically saved as files? In other words, DBFS and SecureFiles go hand in hand mandatorily or SecureFiles can exist without DBFS too?
No.

The words Secure Files should be interpreted that files can safely be stored in the database. This is often safer than storing them on the FileSystem with a reference from the database. If the file is in the database it is also protected by many of the database features. SecureFiles is the modern implementation of LOB's.
The new implementation has a great performance boost compared to the old inplementation.

dbfs is a fileystem that can be created inside the database and that can be mounted on Linux using dbfs_client. Regular operating system processes see it as a regular POSIX filesystem. The LOB's in a dbfs should be implemented as SecureFiles to have the best performance. The performance of dbfs is better than that of NFS, if using filesystem like logging. With normal logging dbfs has about the same performance as NFS, with the added possibility of replicating the data to standby databases.