To familiarize yourself with Outlook on the web, please visit Get help with Outlook on the web and review the section(s) relevant to you:
If you've been granted permission to view another mailbox, you can open it in Outlook on the web.
Please visit Open and use a shared mailbox in Outlook Web App for detailed instructions.
Outlook on the web is a web-based version of Outlook that offers a streamlined, user-friendly interface for managing your Microsoft 365 emails, calendars, and contacts, accessible in your browser.