It totally depends how you configured your Tor.
If it's a relay (meaning you set your ORPort), you can look yourself up in https://atlas.torproject.org/
As for what 'arm' tells you, some relay operators find the arm tool to be useful, and others not so much. It really depends on you. Also note that arm hasn't been updated for some years, so it's starting to show some sharp edges.
And as for why the Tor program is not a relay by default... you might enjoy
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