Click at the link and select the language and time zone.
The change of the default folders names:
If you leave the "Přejmenovat výchozí složky, aby jejich názvy odpovídaly určenému jazyku" checked, then in addition to the Outlook interface language, the basic folders (Inbox, Sent Mail, etc.) will be renamed on the website. This change will be reflected not only on the web but also in email clients. In the case of MS Outlook, this is not a problem, but for some clients, it may lead to duplication of some folders or storage of some messages (e.g., sent or deleted mail) in other folders. If you use clients other than Outlook, we recommend making this change only when you start using Office 365.