You have probably noticed that such words as today, tomorrow, next week, etc. are automatically highlighted in Bitrix24 chats. Click on it to open quick options menu:
create calendar event
Click Create calendar event to add new event to My Calendar. You will see an automated message informing that the event has been successfully added. Click on the active link inside to open the event form. You can edit the event at any time - add guest, change date & time, etc.