How to make a calendar page for every user

You will need to clone the View that provide calendar in /calendar path and add a 'User: User' argument.

In the settings page of this new argument, select 'provide default argument' and then 'user ID from URL' or 'logged in user' as you need.
To add a tab, you will need to give it a path like /user/%/calendar and add a menu tab. This works well if you selected ;User ID from URL'.

I know is too probably too late already, but perhaps for future reference. For Drupal 7, this what you can do:
- setup calendar using views. if you do not know how to do it, refer to the module documentation.
- this calendar is for all users on the site to use

if you want certain individual user to have his own calendar with listed events that he adds himself, and only him can see, and it is listed in tab menu of his user menu, then you can do this:
- clone that calendar views and rename it to something
- on the advance setting, add 'relationships' of 'content:author'
- add 'contextual filter' of 'user:uid'
- change the order of contextual filter so user:uid is listed first
- add to the path: /user/%/calendar.........../month
- do the same thing to week, day and year if you want
- on the menu, choose 'menu tab' and 'user menu'

that will display additional tab on individual user menu.