Calendar on the left isn't showing

By default the calendar is not set to be visible, to enable it, do the following:

Go to options >> display preferences
Scroll down to: Small Calendar Options

And check the box next to:
Small Calendar: show small calendar in left bar

If you would like this to be turned on by default, you will need to edit the default_pref file stored in your data folder. If you've moved this folder make sure you're editing the file in the folder that matches your $data_dir setting in your config_local.php file.

Once you've located the file, edit it and add the following on a new line:

smallcal_show = 1