Clarify benefits of compression methods (ROW_FORMAT=COMPRESSED vs PAGE_COMPRESSED=1)

I am very confused at the moment in relation to how my tables are compressed, and how should I proceed now to ensure I won't have a problem in the future.

I have been compressing a number of tables with ROW_FORMAT=COMPRESSED.

I read the doc page about Compression ( https://mariadb.com/kb/en/library/compression/ ), but I'm still not clear what's the difference between ROW_FORMAT=COMPRESSED and PAGE_COMPRESSED=1.

Can I use both? Is it recommended to use both if I want to benefit from compression?

Is it possible to know what compression algorithms are installed in MariaDB already? (or is it a system-level installation that MariaDB uses?) It's not clear in the documentation.