I have installed eventcalendar extension in civicrm
The fullcalendar is the plugin called "WP Calendar", if you have WordPress you install and activate it in the WordPress plugin area.

For the other issue, you may want to either disable/reinstall the civicrm extension, (works for some people), or take a look at answer to How to use event calendar extension with civievents

Also there is another step that you didn't list, to copy over the folder mentioned in the "Note" section of the README.