Q:

How do I add .htaccess file in my SharePoint Site

Can I use .htaccess file for redirecting and other things in SharePoint 2010 site?
If Yes, tell me how.
If No, Please advice me.

A:

Sharepoint runs on Windows not apache, so doesn't use htaccess. .hta files are not supported by sharepoint. 
There are other ways to redirecting like following:
You can install and use the URL rewrite module for IIS, which is an extension for IIS Server version >7.
Here are some articles about how to use it and create rewrite rules:
http://www.iis.net/learn/extensions/url-rewrite-module/using-the-url-rewrite-module
http://www.iis.net/learn/extensions/url-rewrite-module/creating-rewrite-rules-for-the-url-rewrite-module

