Hey Guys! I have been given a task to convert an already hosted website into responsive. My working knowledge on CSS is below average. In that quest, I heard about media queries. I looked for a solution, but what I got was more confusion. Media Queries...ehh??? I tried responsinator.com and checked my website in that. Actually I don't know how to know whether a website is responsive or not. My website fits the mobile screens. Header and footer automatically adjusts themselves. There is a big ****ing slider and it just got cropped, but still loads images and works fine. If my website is responsive, how come the slider get cropped?

I have a css for my website.
To make a responsive css, will i have to make any changes to the values in my already existing css? Or will I have to just add my styles (without any edits) into the media queries given below.