I have a site called http://www.mysite.com/ configured in apache virtual hosting.
Is it possible to make it use https with free certificate(if required)
Please anyone give me step by step guide
Judging from your earlier questions you seem to use Ubuntu.
Read https://help.ubuntu.com/10.04/serverguide/C/httpd.html#https-configuration on how to configure Apache httpd for HTTPS in Ubuntu.