Webparts are the building blocks of Sharepoint pages. The main aim of webparts are make the contents more moduler and easy to manage.
Webparts and its categort i used as below,
Content Editor - Media and Content
Most used webpart of all the time, almost all the pages i create.
Script Editor - Media and Content
Generally used it for create quick/simple snippet on the fly
Query String (URL) Filter - Filters
Filter the content based on Query String parameter,
Content is most list data.
Current user filter - Filters
Content Search - Content Rollup
Based on the search content metioned on the webpart it pull the data from site level / list level dynamically and give more flexibility over the content by Display template [controller and item template]
Take over the control of all content of the webpart and modify all the sharepoint controls
To be continue ..