Quote from: bob123 on Today at 04:55:43 PM

Because if you have created your wallet, electrum should automatically open that file.
What happens if you go to File -> Recently opened? Do you see your wallet file?

If you have set a password and left file encryption on (the default setting), then Electrum will open the "Electrum - install wizard" screen when you start up:

Quote from: alexlouismorlevat on Today at 04:33:38 PM

Isn't there a file somewhere in my local macOS that is my wallet and that I can copy to a USB key?

Yes, if you click the "Choose..." button on the screen above, it will open the directory containing all the wallet files that have been created.

Quote from: alexlouismorlevat on Today at 04:33:38 PM

I saved the seed of the wallet. Is it really the only thing we need to restore a wallet in case of computer failure?
Only with Electrum or does it work with every software or online service?

Yes, the 12 word seed mnemonic is all you need to recover. This 12 word seed is specific to Electrum, it will not work in 99.9% of other wallet software (I believe there are 1 or 2 other wallets that support Electrum seeds, but they are the exception, not the rule).

Quote from: alexlouismorlevat on Today at 04:33:38 PM

If you have links to tutorials to help me understand how all this works. I would appreciate it because I understand NOT MUCH...... except that I need to keep the seed safe.

Maybe have a read through some of the guides here: https://bitcoinelectrum.com/

They might explain some of the questions you have. Alternatively, the electrum docs are here: https://electrum.readthedocs.io/en/latest/

Quote from: alexlouismorlevat on Today at 04:33:38 PM

I would feel safer storing my BTC on an online service but everyone says it's a bad idea... Right?

Ask the people who have funds stuck in Cryptopia how leaving coins on an online service worked out for them so far: https://bitcointalk.org/index.php?topic=1669443.new#new
or the users of Mt. Gox...
or the users of the countless other services that got hacked/closed unexpectedly...

"Not your keys, NOT your Bitcoin"