How to create a template file for Categories? below is my categories url.

http://example.com/index.php?p=categories/vaporizers

i create a template files for categories like

templates/categories/index.html
templates/categories/_entry.html


my index.html is not called when categories view. please tell me where i create a mistake.

Thanks
When you create a category you will need to tell craft which template to load:



So for your example you would put categories/index in there and you should find the template gets loaded when you visit the category url.

See more about templating in the docs