I'm not sure I understand you correctly. That's why I'm rephrasing what you said:
You've got an account with multiple aliases: xxx@web.com and mizu@web.com. At the moment both addresses are received in the Inbox (French: Réception) and you want to receive messages to mizu@web.com in a different folder. You can do that with a filter.
Select a message addressed to mizu@web.com
From the menu pick:
Specials -> Create filter...
Uncheck 'sender' and check 'recipient'
Next to 'recipient' you should see ' mizu@web.com'
Next to 'Move to folder' you see the folder where the filter wants to move its messages, but as that defaults to something related to the sende, I can imagine that you want to change to something like mizu, you can do that by pressing the folder tree icon at the right, this eanbles you to create a new folder right then.

The directions in this message (and all messages on this forum) presume you're using the English interface. You can switch to the English interface via the menu:
Options -> Langue -> Anglais
You switch back to French via:
Options -> Language -> French

I'm again not sure about what you want. Do you want to use the second account from two computers? In that case you need to create the account on the second system too.
When you want to share the message base between both computers, then you need to create the account on the second computer too, but you need to be sure that you use the same name for the new account, this will cause TB to recognise the settings.
When you mean something else altogether then you need to be more explicit in your wishes.