Can't get rid of Categories, Search form, Meta etc from Sidebar of the pages?

That's actually our theme's default widgets that appear if none of your widgets placed in Primary/Secondary widget areas.

To remove them, just visit your Dashboard->Appearance->Widgets and place a Blank Text widget or your desired widget under Primary/Secondary Widget Areas.

You can also refer this tutorial link: https://www.inkthemes.com/how-to-use-widgets-in-wordpress/