You can also get to this Quick Start Guide in the WordPress back end by going to Help -> Getting Started. It is meant to quickly give you the basics on how to use the My Calendar plugin.
After activating My Calendar, a new default “My Calendar” page will automatically be created. The Calendar Page Location can be changed through the Settings > General screen.
The primary My Calendar Page is a standard WordPress Page, and can be edited in the same way as any calendar page. If you delete the page, you will need to assign a new calendar page. The plugin will mostly work without a primary calendar page, but there are some functions that depend on knowing where the plugin can be found on your site.

Customize your calendar
Go to My Calendar page. You’ll find it in your Pages list at WordPress > Pages. It will be named “My Calendar” and have a flag indicating that it’s your primary page.
At the bottom of the editor, you’ll find the My Calendar Display Options (click the arrow to open). This is a way to set the defaults of how your calendar will look on the front end. Go to My Calendar Display Options documentation to learn more about these options.

Add Events
Go to My Calendar > Add Event to create new events.
Add Categories
Go to My Calendar > Categories to add categories and change the category color or icon for your categories.
Add Locations
Go to My Calendar > Locations to add locations.